BaseFilter: allow to remove non-existent tags

With notmuch2 bindings, removing a non-existing tag raises a KeryError.
Catch that to allow the same filter usage as with legacy bindings.

Suggested-By: Toke Høiland-Jørgensen <[email protected]>

Author: mjg

afew/filters/BaseFilter.py

@@ -102,6 +102,9 @@ def commit(self, dry_run=True):
                     message.tags.add(tag)
 
                 for tag in self._remove_tags.get(message_id, []):
-                    message.tags.remove(tag)
+                    try:
+                        message.tags.remove(tag)
+                    except KeyError:
+                        pass
 
         self.flush_changes()