Disable systemui navigation events while keyguard is showing

This feature isn't generally useful on this screen and provides
an additional mechanism for falsing, so it should be disabled.

Fixes bug 30443528

Change-Id: Ibdba485917b5e66780ff4915f48ff2014f195eca

packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java

@@ -2620,7 +2620,8 @@ public class PhoneStatusBar extends BaseStatusBar implements DemoMode,
     @Override
     public void handleSystemNavigationKey(int key) {
         if (SPEW) Log.d(TAG, "handleSystemNavigationKey: " + key);
-        if (!panelsEnabled() || !mKeyguardMonitor.isDeviceInteractive()) {
+        if (!panelsEnabled() || !mKeyguardMonitor.isDeviceInteractive()
+                || mKeyguardMonitor.isShowing()) {
             return;
         }