sync configuration off main thread

Signal/src/ViewControllers/ThreadSettings/OWSConversationSettingsViewController.m

@@ -1271,10 +1271,12 @@ const CGFloat kIconViewLength = 24;
     [self updateTableContents];
     [self.conversationSettingsViewDelegate conversationColorWasUpdated];
 
+    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
         ConversationConfigurationSyncOperation *operation =
             [[ConversationConfigurationSyncOperation alloc] initWithThread:self.thread];
         OWSAssert(operation.isReady);
         [operation start];
+    });
 
     [self dismissViewControllerAnimated:YES completion:nil];
 }