Fix java.lang.ArrayIndexOutOfBoundsException at ArraySet in...

Fix java.lang.ArrayIndexOutOfBoundsException at ArraySet in GenericWindowPolicyController.onRunningAppsChanged()

- Before iterating over mRunningAppsChangedListener, we need to confirm
  whether there is a listener in mRunningAppsChangedListener to avoid
  ArrayIndexOutOfBoundsException.
- Use mGenericWindowPolicyControllerLock to protect
  mRunningAppsChangedListener access.

Bug: 248192490
Test: Manual
Change-Id: Iedd031f50659f027576086788392110a3432858a