SystemUI: fix NPE when configuring blur layer

I noticed a NPE on my device with OOB encryption & password lockscreen
(no password required to boot).  This fixes it.

FEIJ-753

Change-Id: I303354e94be451ab65deb815ecf39cda9d6a339e

Author: Scott Mertz

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

@@ -148,7 +148,7 @@ private void applyKeyguardFlags(State state) {
         } else {
             mLpChanged.flags &= ~WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER;
             mLpChanged.privateFlags &= ~WindowManager.LayoutParams.PRIVATE_FLAG_KEYGUARD;
-            if (mKeyguardBlurEnabled) {
+            if (mKeyguardBlurEnabled && mKeyguardBlur != null) {
                 mKeyguardBlur.hide();
             }
         }