use a background thread for closing the camera on pause

app/src/main/kotlin/com/simplemobiletools/camera/activities/MainActivity.kt

@@ -99,8 +99,11 @@ class MainActivity : SimpleActivity(), PhotoProcessor.MediaSavedListener {
         if (mPreview?.getCameraState() == STATE_PICTURE_TAKEN) {
             toast(R.string.photo_not_saved)
         }
+
+        ensureBackgroundThread {
             mPreview?.onPaused()
         }
+    }
 
     override fun onDestroy() {
         super.onDestroy()