Prevent creating empty sidecar directories

frontend/apps/filemanager/filemanagerbookinfo.lua

@@ -59,6 +59,9 @@ function BookInfo:show(file, book_props)
     -- book_props may be provided if caller already has them available
     -- but it may lack 'pages', that we may get from sidecar file
     if not book_props or not book_props.pages then
+        -- check there is actually a sidecar file before calling DocSettings:open()
+        -- that would create an empty sidecar directory
+        if DocSettings:hasSidecarFile(file) then
             local doc_settings = DocSettings:open(file)
             if doc_settings then
                 if not book_props then
@@ -85,6 +88,7 @@ function BookInfo:show(file, book_props)
                 end
             end
         end
+    end
 
     -- If still no book_props (book never opened or empty 'stats'), open the
     -- document to get them