Bug 1750142 - Don't return nullptr for LockScreenOrientation. r=geckoview-reviewers,calu

We should return rejected promise instead of `nullptr` to make simple.

Differential Revision: https://phabricator.services.mozilla.com/D135980

hal/android/AndroidHal.cpp

@@ -128,7 +128,8 @@ RefPtr<MozPromise<bool, bool, false>> LockScreenOrientation(
       }
     }
     default:
-      return nullptr;
+      NS_WARNING("Unsupported screen orientation type");
+      return MozPromise<bool, bool, false>::CreateAndReject(false, __func__);
   }
 }