Always initialize the _weakFactory in FlutterViewController (flutter#32395)

Fixes flutter#101209

Author: jason-simmons

shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -195,6 +195,7 @@ - (void)sharedSetupWithProject:(nullable FlutterDartProject*)project
     project = [[[FlutterDartProject alloc] init] autorelease];
   }
   FlutterView.forceSoftwareRendering = project.settings.enable_software_rendering;
+  _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
   auto engine = fml::scoped_nsobject<FlutterEngine>{[[FlutterEngine alloc]
                 initWithName:@"io.flutter"
                      project:project
@@ -206,7 +207,6 @@ - (void)sharedSetupWithProject:(nullable FlutterDartProject*)project
   }
 
   _viewOpaque = YES;
-  _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
   _engine = std::move(engine);
   _flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
   [_engine.get() createShell:nil libraryURI:nil initialRoute:initialRoute];