show a warning about missing widgets if the app is installed on an sd card

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

@@ -99,6 +99,8 @@ class MainActivity : SimpleActivity(), RefreshRecyclerViewListener {
         if (!checkOpenIntents()) {
             updateViewPager()
         }
+
+        checkAppOnSDCard()
     }
 
     override fun onResume() {