Prevent bogus message emission on group deletion

Only send a message if the local number is part of the group

* Fix error on empty group #1449
* Fix an unlogged issue about notification sent to group members even is the local user already quit the group

Signal/src/view controllers/SignalsViewController.m

@@ -332,6 +332,9 @@
 - (void)tableViewCellTappedDelete:(NSIndexPath *)indexPath {
     TSThread *thread = [self threadForIndexPath:indexPath];
     if ([thread isKindOfClass:[TSGroupThread class]]) {
+
+        TSGroupThread *gThread = (TSGroupThread *)thread;
+        if ([gThread.groupModel.groupMemberIds containsObject:[TSAccountManager localNumber]]) {
             UIAlertController *removingFromGroup = [UIAlertController
                                                     alertControllerWithTitle:[NSString
                                                                               stringWithFormat:NSLocalizedString(@"GROUP_REMOVING", nil), [thread name]]
@@ -361,6 +364,9 @@
         } else {
             [self deleteThread:thread];
         }
+    } else {
+        [self deleteThread:thread];
+    }
 }
 
 - (void)deleteThread:(TSThread *)thread {