Ignore duplicate keyguardGoingAway request.

SysUI calls ActivityTaskManager#keyguardGoingAway to start keyguard
going away process. In case SysUI calls the binder call again while
keyguard is going away, ActivityTaskManager ignores it.

Bug: 215201490
Test: atest KeyguardTransitionTests
Change-Id: Iaee8c7cd25f0a89c5e90bd6fc0185dd54fb1d99e

services/core/java/com/android/server/wm/KeyguardController.java

@@ -235,7 +235,7 @@ class KeyguardController {
      */
     void keyguardGoingAway(int displayId, int flags) {
         final KeyguardDisplayState state = getDisplayState(displayId);
-        if (!state.mKeyguardShowing) {
+        if (!state.mKeyguardShowing || state.mKeyguardGoingAway) {
             return;
         }
         Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, "keyguardGoingAway");