Set wrapper sdk type before calling initialize

* Set the wrapper SDK type first so when initialize is called, the native SDK can check if the SDK is a wrapper type in order to conditionally omit a misleading fatal log
* See OneSignal/OneSignal-iOS-SDK#1468

Author: nan-li

ios/Classes/OneSignalPlugin.m

@@ -56,10 +56,10 @@ + (instancetype)sharedInstance {
 #pragma mark FlutterPlugin
 + (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
 
-    [OneSignal initialize:nil withLaunchOptions:nil];
     OneSignalWrapper.sdkType = @"flutter";
     OneSignalWrapper.sdkVersion = @"050202";
-    
+    [OneSignal initialize:nil withLaunchOptions:nil];
+
     OneSignalPlugin.sharedInstance.channel = [FlutterMethodChannel
                                      methodChannelWithName:@"OneSignal"
                                      binaryMessenger:[registrar messenger]];