[local_auth] The alert should be called in the main thread.

packages/local_auth/ios/Classes/FLTLocalAuthPlugin.m

@@ -62,9 +62,15 @@ - (void)alertMessage:(NSString *)message
                 }];
     [alert addAction:additionalAction];
   }
-  [[UIApplication sharedApplication].delegate.window.rootViewController presentViewController:alert
-                                                                                     animated:YES
-                                                                                   completion:nil];
+
+  @try {
+      dispatch_async(dispatch_get_main_queue(), ^{
+          [[UIApplication sharedApplication].delegate.window.rootViewController presentViewController:alert  animated:YES  completion:nil];
+      });
+  } @catch (NSException *exception) {
+      NSLog(@"Exception presentViewController: %@", exception);
+  } @finally {
+  }
 }
 
 - (void)getAvailableBiometrics:(FlutterResult)result {