AndroidSClockController: fix NPE in setSlice

E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.widget.TextClock.getId()' on a null object reference
E AndroidRuntime:	at com.android.keyguard.clock.AndroidSClockController.setSlice(AndroidSClockController.java:379)

Signed-off-by: Chenyang Zhong <zhongcy95@gmail.com>
Change-Id: Ie23ab0008362a8b95f303fdfb17fcb9759c0ad05

Author: jjpprrrr

packages/SystemUI/src/com/android/keyguard/clock/AndroidSClockController.java

@@ -377,8 +377,12 @@ public void setSlice(Slice slice) {
         mTitle.requestLayout();
         mRow.requestLayout();
 
-        mRowHeight = mRow.getHeight() + (mHasHeader ? mTitle.getHeight() : 0);
-        if (mRow.getChildCount() != 0) mContainerSetBig.setMargin(mClock.getId(), ConstraintSet.TOP, mRowHeight);
+        if (mClock != null) {
+            mRowHeight = mRow.getHeight() + (mHasHeader ? mTitle.getHeight() : 0);
+            if (mRow.getChildCount() != 0) {
+                mContainerSetBig.setMargin(mClock.getId(), ConstraintSet.TOP, mRowHeight);
+            }
+        }
     };
 
     /**