Don't pass null to memcmp.

tests/PathTest.cpp

Index: tests/PathTest.cpp
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index bc3a3d7bdb5874ffbd3156ae309d73f9562b8da3..94b91d261be37a3396f184f28202de836dfbb26b 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -3435,7 +3435,11 @@ static void compare_dump(skiatest::Reporter* reporter, const SkPath& path, bool
     path.dump(&wStream, force, dumpAsHex);
     SkAutoDataUnref data(wStream.copyToData());
     REPORTER_ASSERT(reporter, data->size() == strlen(str));
-    REPORTER_ASSERT(reporter, !memcmp(data->data(), str, strlen(str)));
+    if (strlen(str) > 0) {
+        REPORTER_ASSERT(reporter, !memcmp(data->data(), str, strlen(str)));
+    } else {
+        REPORTER_ASSERT(reporter, data->data() == NULL || !memcmp(data->data(), str, strlen(str)));
+    }
 }
 
 static void test_dump(skiatest::Reporter* reporter) {