Fix NPE in AccServ.onAccessibilityEvent

[Meems33]

Add NPE guard to prevent errors on AccessibilityEvents that do not have context about a package

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Object.equals(java.lang.Object)' on a null object reference
    at com.baronkiko.launcherhijack.AccServ.onAccessibilityEvent(AccServ.java:31)
    at android.accessibilityservice.AccessibilityService$2.onAccessibilityEvent(AccessibilityService.java:1538)
    at android.accessibilityservice.AccessibilityService$IAccessibilityServiceClientWrapper.executeMessage(AccessibilityService.java:1724)
    at com.android.internal.os.HandlerCaller$MyHandler.handleMessage(HandlerCaller.java:37)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6734)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)