fix(gotrue): allow empty session response for verifyOtp method (supabase#680)

fix: allow empty session response for verifyOtp method

Author: dshukertjr

packages/gotrue/lib/src/gotrue_client.dart

@@ -495,15 +495,11 @@ class GoTrueClient {
 
     final authResponse = AuthResponse.fromJson(response);
 
-    if (authResponse.session == null) {
-      throw AuthException(
-        'An error occurred on token verification.',
-      );
+    if (authResponse.session != null) {
+      _saveSession(authResponse.session!);
+      _notifyAllSubscribers(AuthChangeEvent.signedIn);
     }
 
-    _saveSession(authResponse.session!);
-    _notifyAllSubscribers(AuthChangeEvent.signedIn);
-
     return authResponse;
   }