fix: prevent crash when activity is finishing or destroyed (#218)

app/src/main/kotlin/org/fossify/notes/activities/MainActivity.kt

@@ -565,6 +565,10 @@ class MainActivity : SimpleActivity() {
 
     private fun initViewPager(wantedNoteId: Long? = null) {
         NotesHelper(this).getNotes { notes ->
+            if (isFinishing || isDestroyed) {
+                return@getNotes
+            }
+
             notes.filter { it.shouldBeUnlocked(this) }
                 .forEach(::removeProtection)