Fix bug #10205316 CTS (KLP): android.graphics tests are failing

- fix null Shader case during copy

Related to https://googleplex-android-review.googlesource.com/#/c/336815/7

Change-Id: I920d6bb181ddb92d6f771e5060fd1858430e71ad

graphics/java/android/graphics/Paint.java

@@ -431,6 +431,8 @@ public class Paint {
         mRasterizer = paint.mRasterizer;
         if (paint.mShader != null) {
             mShader = paint.mShader.copy();
+        } else {
+            mShader = null;
         }
         mTypeface = paint.mTypeface;
         mXfermode = paint.mXfermode;