Fix crash if drawable doesn't have constant state

Change-Id: I2364efb9dc1446bc1a8c50abf6bd34a73c226f7e
Fixes: 31755893
diff --git a/core/java/com/android/internal/policy/BackdropFrameRenderer.java b/core/java/com/android/internal/policy/BackdropFrameRenderer.java
index 619303f..1abb59b 100644
--- a/core/java/com/android/internal/policy/BackdropFrameRenderer.java
+++ b/core/java/com/android/internal/policy/BackdropFrameRenderer.java
@@ -110,12 +110,15 @@
             int statusBarColor, int navigationBarColor) {
         mDecorView = decorView;
         mResizingBackgroundDrawable = resizingBackgroundDrawable != null
+                        && resizingBackgroundDrawable.getConstantState() != null
                 ? resizingBackgroundDrawable.getConstantState().newDrawable()
                 : null;
         mCaptionBackgroundDrawable = captionBackgroundDrawableDrawable != null
+                        && captionBackgroundDrawableDrawable.getConstantState() != null
                 ? captionBackgroundDrawableDrawable.getConstantState().newDrawable()
                 : null;
         mUserCaptionBackgroundDrawable = userCaptionBackgroundDrawable != null
+                        && userCaptionBackgroundDrawable.getConstantState() != null
                 ? userCaptionBackgroundDrawable.getConstantState().newDrawable()
                 : null;
         if (mCaptionBackgroundDrawable == null) {