Custom cover: fix (#10513)

Somehow have overlooked in testing.
Closes #10512.

frontend/apps/filemanager/filemanagerbookinfo.lua

@@ -358,10 +358,10 @@ function BookInfo:setCustomBookCover(file, book_props, metadata_updated_caller_c
                 if sidecar_file then
                     sidecar_dir = util.splitFilePathName(sidecar_file)
                 else -- no sdr folder, create new
-                    sidecar_dir = DocSettings:getSidecarDir(file)
+                    sidecar_dir = DocSettings:getSidecarDir(file) .. "/"
                     util.makePath(sidecar_dir)
                 end
-                local new_cover_file = sidecar_dir .. "/" .. "cover." .. util.getFileNameSuffix(image_file)
+                local new_cover_file = sidecar_dir .. "cover." .. util.getFileNameSuffix(image_file)
                 if ffiutil.copyFile(image_file, new_cover_file) == nil then
                     kvp_update()
                 end

frontend/docsettings.lua

@@ -299,10 +299,13 @@ function DocSettings:flush(data, no_cover)
             -- move cover file to the metadata file location
             if not no_cover then
                 local cover_file = self:getCoverFile()
-                if cover_file and util.splitFilePathName(cover_file) ~= sidecar_dir then
-                    ffiutil.copyFile(cover_file, sidecar_dir)
-                    os.remove(cover_file)
-                    self:getCoverFile(true) -- reset cache
+                if cover_file then
+                    local filepath, filename = util.splitFilePathName(cover_file)
+                    if filepath ~= sidecar_dir .. "/" then
+                        ffiutil.copyFile(cover_file, sidecar_dir .. "/" .. filename)
+                        os.remove(cover_file)
+                        self:getCoverFile(true) -- reset cache
+                    end
                 end
             end