Harden offline region deletion

platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/offline/OfflineRegion.java

@@ -358,10 +358,10 @@ public void run() {
    */
   public void delete(@NonNull final OfflineRegionDeleteCallback callback) {
     if (!isDeleted) {
+      isDeleted = true;
       deleteOfflineRegion(new OfflineRegionDeleteCallback() {
         @Override
         public void onDelete() {
-          isDeleted = true;
           getHandler().post(new Runnable() {
             @Override
             public void run() {
@@ -376,6 +376,7 @@ public void onError(final String error) {
           getHandler().post(new Runnable() {
             @Override
             public void run() {
+              isDeleted = false;
               callback.onError(error);
             }
           });