coverbrowser: quicker extraction of EPUB metadata (#3736)

bump crengine:
Allow for quicker loading when interested in metadata only.
Allow for more than 65535 different attribute values.
Increase gamma values range.

base

@@ -1 +1 @@
-Subproject commit 20b7d0724f151966c2b436095455bcb9bf05076b
+Subproject commit c6e497a310e95def50a8aae9aad02da9cc0e0424

frontend/document/credocument.lua

@@ -132,9 +132,10 @@ function CreDocument:init()
     self.info.configurable = true
 end
 
-function CreDocument:loadDocument()
+function CreDocument:loadDocument(full_document)
     if not self._loaded then
-        if self._document:loadDocument(self.file) then
+        local only_metadata = full_document == false
+        if self._document:loadDocument(self.file, only_metadata) then
             self._loaded = true
         end
     end

plugins/coverbrowser.koplugin/bookinfomanager.lua

@@ -372,7 +372,7 @@ function BookInfoManager:extractBookInfo(filepath, cover_specs)
             -- Setting a default font before loading document
             -- actually do prevent some crashes
             document:setFontFace(document.default_font)
-            if not document:loadDocument() then
+            if not document:loadDocument(false) then -- load only metadata
                 -- failed loading, calling other methods would segfault
                 loaded = false
             end