Merge pull request #806 from OneSignal/fix/resolve_request_permission

[fix] Android: Resolve `requestPermission` call when already granted

Author: nan-li

android/src/main/java/com/onesignal/flutter/OneSignalNotifications.java

@@ -78,6 +78,12 @@ else if (call.method.contentEquals("OneSignal#addNativeClickListener"))
 
     private void requestPermission(MethodCall call, Result result) {
         boolean fallback = (boolean) call.argument("fallbackToSettings");
+        // if permission already exists, return early as the method call will not resolve
+        if (OneSignal.getNotifications().getPermission()) {
+            replySuccess(result, true);
+            return;
+        }
+
         OneSignal.getNotifications().requestPermission(fallback, Continue.with(permissionResult -> {
             replySuccess(result, permissionResult.getData());
         }));