make sure that sanitize_mpdtag always returns a number (regardless of…

… type int or str)

sonata.py

@@ -3371,6 +3371,7 @@ def download_image_to_filename(self, artist, album, dest_filename, all_images=Fa
         try:
             img_url = ""
             self.downloading_image = True
+            # Amazon currently doesn't support utf8 and suggests latin1 encoding instead:
             try:
                 artist = urllib.quote(artist.encode('latin1'))
                 album = urllib.quote(album.encode('latin1'))
@@ -6888,7 +6889,7 @@ def sanitize_mpdtag(self, mpdtag, return_int=False, str_padding=0):
                 if return_int:
                     return 0
                 else:
-                    return ""
+                    return "0".zfill(str_padding)
 
     def searchfilter_toggle(self, widget, initial_text=""):
         if self.filterbox_visible: