Fix getAttributeSetSourceResId to AttributeSet created from null.

Xml.asAttributeSet with a null returns non XmlBlock.Parser type
object.
This fixes the existing test that broke due to my changes to
LayoutInflater.

Test: atest CtsViewTestCases:LayoutInflaterTest
Change-Id: Ib10e07ef3814c5570a6d2bd334481f2e26bb3d3e

core/java/android/content/res/ResourcesImpl.java

@@ -1303,7 +1303,7 @@ public class ResourcesImpl {
 
     @AnyRes
     static int getAttributeSetSourceResId(@Nullable AttributeSet set) {
-        if (set == null) {
+        if (set == null || !(set instanceof XmlBlock.Parser)) {
             return ID_NULL;
         }
         return ((XmlBlock.Parser) set).getSourceResId();