In beet modify: don't ask for confirmation if there is nothing to do

beets/ui/commands.py

@@ -1155,6 +1155,11 @@ def modify_items(lib, mods, query, write, move, album, confirm):
             if _showdiff(field, obj.get(field), value):
                 changed.add(obj)
 
+    # Still something to do?
+    if not changed:
+        print_('No modification to perform.')
+        return
+    else:
         # Confirm.
         if confirm:
             extra = ' and write tags' if write else ''