avoid running 2 media fetching asynctasks

app/src/main/kotlin/com/simplemobiletools/gallery/activities/MediaActivity.kt

@@ -378,6 +378,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         }
 
         mLoadedInitialPhotos = true
+        mCurrAsyncTask?.stopFetching()
         mCurrAsyncTask = GetMediaAsynctask(applicationContext, mPath, mIsGetVideoIntent, mIsGetImageIntent, mShowAll) {
             gotMedia(it)
         }