[plugin] Exporter: use util.getSafeFilename() to remove illegal characters from output filename (#10282)

Fixes #10281.

plugins/exporter.koplugin/base.lua

@@ -93,7 +93,7 @@ function BaseExporter:getFilePath(t)
     if not self.is_remote then
         local filename = string.format("%s-%s.%s",
             self:getTimeStamp(),
-            #t == 1 and t[1].exportable_title or "all-books",
+            #t == 1 and t[1].output_filename or "all-books",
             self.extension)
         return self.clipping_dir .. "/" .. getSafeFilename(filename)
     end

plugins/exporter.koplugin/clip.lua

@@ -394,8 +394,8 @@ function MyClipping:getDocMeta(view)
     end
     return {
         title = title,
-        -- To make sure that export doesn't fail due to unsupported charchters.
-        exportable_title = parsed_title,
+        -- Replaces characters that are invalid in filenames.
+        output_filename = util.getSafeFilename(title),
         author = author,
         number_of_pages = number_of_pages,
         file = view.document.file,