quick_frontend: catch an exception that can occurs when using a concurrent client

frontends/src/quick_frontend/quick_contact_list.py

@@ -390,7 +390,10 @@ class QuickContactList(QuickWidget):
         except KeyError:
             log.warning(_(u"Trying to delete an unknow entity [{}]").format(entity))
         if in_roster:
-            self._roster.remove(entity_bare)
+            try:
+                self._roster.remove(entity_bare)
+            except KeyError:
+                pass  # contact has been removed already from a concurrent client?
         del self._cache[entity_bare]
         for group in groups:
             self._groups[group]['jids'].remove(entity_bare)