fix a small bug that seldom leaded a crash

Author: ExploiTR

app/src/main/java/spacehunn/exploitr/deautherwebgui/MainActivity.java

@@ -249,7 +249,7 @@ public void onReceive(Context c, Intent ix) {
         iFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
         getApplicationContext().registerReceiver(reaver, iFilter);
 
-        new AlertDialog.Builder(MainActivity.this)
+       AlertDialog.Builder x = new AlertDialog.Builder(MainActivity.this)
                 .setView(scanView)
                 .setCancelable(false)
                 .setNeutralButton("Help", new DialogInterface.OnClickListener() {
@@ -265,8 +265,10 @@ public void onClick(DialogInterface dialog, int which) {
                     public void onClick(DialogInterface dialog, int which) {
                         getApplicationContext().unregisterReceiver(reaver);
                     }
-                })
-                .show();
+                });
+        if (!MainActivity.this.isFinishing()) {
+            x.show();
+        }
     }
 
     @Override