Trying to be consistent when members are allowed to be NULL

src/core/SkLocalMatrixShader.cpp

Index: src/core/SkLocalMatrixShader.cpp
diff --git a/src/core/SkLocalMatrixShader.cpp b/src/core/SkLocalMatrixShader.cpp
index 62840dd3af63e51a7c5b269fe645488492fd2b43..a7d2c15b0c072e75240ec686455f28b5f0abb8ed 100644
--- a/src/core/SkLocalMatrixShader.cpp
+++ b/src/core/SkLocalMatrixShader.cpp
@@ -60,6 +60,10 @@ void SkLocalMatrixShader::toString(SkString* str) const {
 #endif
 
 SkShader* SkShader::CreateLocalMatrixShader(SkShader* proxy, const SkMatrix& localMatrix) {
+    if (NULL == proxy) {
+        return NULL;
+    }
+
     if (localMatrix.isIdentity()) {
         return SkRef(proxy);
     }