show alert must happen in main thread (#1119)

//freebie

Signal/src/view controllers/MessageComposeTableViewController.m

@@ -479,13 +479,13 @@
           });
         }
         failure:^(NSError *error) {
+            dispatch_async(dispatch_get_main_queue(), ^{
                 UIAlertView *alert = [[UIAlertView alloc] initWithTitle:TIMEOUT
                                                                 message:TIMEOUT_CONTACTS_DETAIL
                                                                delegate:nil
                                                       cancelButtonTitle:NSLocalizedString(@"OK", @"")
                                                       otherButtonTitles:nil];
                 [alert show];
-          dispatch_async(dispatch_get_main_queue(), ^{
                 [self updateAfterRefreshTry];
           });
         }];