CoverBrowser: speedup "View full size cover"

It was doing a full document load to get the cover. It now does
the faster "only metadata" load.
Also move the trick of setting a default font in CreDocument, so
that all callers of document:loadDocument(false) benefit from it.
Prevent crash when no cover image is available (even if the cache
says it has one, the file may have been updated and doesn't have
it anymore).

frontend/document/credocument.lua

@@ -177,6 +177,11 @@ function CreDocument:loadDocument(full_document)
     if not self._loaded then
         local only_metadata = full_document == false
         logger.dbg("CreDocument: loading document...")
+        if only_metadata then
+            -- Setting a default font before loading document
+            -- actually do prevent some crashes
+            self:setFontFace(self.default_font)
+        end
         if self._document:loadDocument(self.file, only_metadata) then
             self._loaded = true
             logger.dbg("CreDocument: loading done.")

plugins/coverbrowser.koplugin/bookinfomanager.lua

@@ -391,9 +391,6 @@ function BookInfoManager:extractBookInfo(filepath, cover_specs)
     if document then
         local pages
         if document.loadDocument then -- needed for crengine
-            -- Setting a default font before loading document
-            -- actually do prevent some crashes
-            document:setFontFace(document.default_font)
             if not document:loadDocument(false) then -- load only metadata
                 -- failed loading, calling other methods would segfault
                 loaded = false

plugins/coverbrowser.koplugin/covermenu.lua

@@ -1,6 +1,7 @@
 local DocumentRegistry = require("document/documentregistry")
 local FileManagerBookInfo = require("apps/filemanager/filemanagerbookinfo")
 local ImageViewer = require("ui/widget/imageviewer")
+local InfoMessage = require("ui/widget/infomessage")
 local Menu = require("ui/widget/menu")
 local TextViewer = require("ui/widget/textviewer")
 local UIManager = require("ui/uimanager")
@@ -127,7 +128,6 @@ function CoverMenu:updateItems(select_number)
                     UIManager:unschedule(self.items_update_action)
                     self.items_update_action = nil
                 end
-                local InfoMessage = require("ui/widget/infomessage")
                 UIManager:show(InfoMessage:new{
                     text = _("Start-up of background extraction job failed.\nPlease restart KOReader or your device.")
                 })
@@ -232,13 +232,22 @@ function CoverMenu:updateItems(select_number)
                         callback = function()
                             local document = DocumentRegistry:openDocument(file)
                             if document then
+                                if document.loadDocument then -- needed for crengine
+                                    document:loadDocument(false) -- load only metadata
+                                end
                                 local cover_bb = document:getCoverPageImage()
-                                local imgviewer = ImageViewer:new{
-                                    image = cover_bb,
-                                    with_title_bar = false,
-                                    fullscreen = true,
-                                }
-                                UIManager:show(imgviewer)
+                                if cover_bb then
+                                    local imgviewer = ImageViewer:new{
+                                        image = cover_bb,
+                                        with_title_bar = false,
+                                        fullscreen = true,
+                                    }
+                                    UIManager:show(imgviewer)
+                                else
+                                    UIManager:show(InfoMessage:new{
+                                        text = _("No cover image available."),
+                                    })
+                                end
                                 UIManager:close(self.file_dialog)
                                 DocumentRegistry:closeDocument(file)
                             end
@@ -352,13 +361,22 @@ function CoverMenu:onHistoryMenuHold(item)
             callback = function()
                 local document = DocumentRegistry:openDocument(file)
                 if document then
+                    if document.loadDocument then -- needed for crengine
+                        document:loadDocument(false) -- load only metadata
+                    end
                     local cover_bb = document:getCoverPageImage()
-                    local imgviewer = ImageViewer:new{
-                        image = cover_bb,
-                        with_title_bar = false,
-                        fullscreen = true,
-                    }
-                    UIManager:show(imgviewer)
+                    if cover_bb then
+                        local imgviewer = ImageViewer:new{
+                            image = cover_bb,
+                            with_title_bar = false,
+                            fullscreen = true,
+                        }
+                        UIManager:show(imgviewer)
+                    else
+                        UIManager:show(InfoMessage:new{
+                            text = _("No cover image available."),
+                        })
+                    end
                     UIManager:close(self.histfile_dialog)
                     DocumentRegistry:closeDocument(file)
                 end