Fix leaked windows exception in WifiDialogActivity

WifiDialog was created by WifiDialogActivity.
If activity was destroyed suddenly, WifiDialog can't dismiss itself.

So, we need to dismiss dialog, when activity was destroyed.

Test: robo and manual test
Bug: 111841375
Change-Id: I8aaf1c78e72144bf7c9cbc2392bce30e715d86e9
1 file changed