Disable shadow drawing for empty/null outlines

Change-Id: I60d0f326cfab97d88c49d17cf32e619b5e60b94a
diff --git a/libs/hwui/Outline.h b/libs/hwui/Outline.h
index 5c24335..5e7f899 100644
--- a/libs/hwui/Outline.h
+++ b/libs/hwui/Outline.h
@@ -49,6 +49,10 @@
         mBounds.set(outline->getBounds());
     }
 
+    bool isEmpty() const {
+        return mType == kOutlineType_None;
+    }
+
     void setEmpty() {
         mType = kOutlineType_None;
         mPath.reset();