Merge pull request #43 from rickytheoldtree/newmigration

Singleton in SignInHelperObject.cs Fix

Author: Thaina

GoogleSignIn/Impl/SignInHelperObject.cs

@@ -27,6 +27,9 @@ public class SignInHelperObject : MonoBehaviour {
 
     internal static SignInHelperObject Instance {
       get {
+        if (instance) {
+          return instance;
+        }
         if (Application.isPlaying) {
           // add an invisible game object to the scene
           GameObject obj = new GameObject("GoogleSignInHelperObject");