Fix Check PIN during upgrade to v7 crash (#364)

* Fix crash caused by showing CheckPinDuringUpgradeDialog after finishing AppUpgradeActivity
* This crash happens during an update from v6 and the user puts the enter PIN screen to the background after entering the PIN incorrectly 3 times and is required to wait a minute.

wallet/src/de/schildbach/wallet/ui/AppUpgradeActivity.kt

@@ -64,10 +64,18 @@ class AppUpgradeActivity : AppCompatActivity() {
         configuration.pinLength = PinPreviewView.CUSTOM_PIN_LENGTH
 
         pinRetryController = PinRetryController.getInstance()
+    }
 
+    override fun onStart() {
+        super.onStart()
         temporaryLockCheckRunnable.run()
     }
 
+    override fun onStop() {
+        super.onStop()
+        temporaryLockCheckHandler.removeCallbacks(temporaryLockCheckRunnable)
+    }
+
     private fun askForPin() {
         title_pane.visibility = View.INVISIBLE
         dash_logo.visibility = View.INVISIBLE