Don't pass null to memcmp.

tests/PathTest.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkPaint.h"
 #include "SkParse.h"
@@ skipping 3417 matching lines @@
     a.lineTo(1, 2);
     REPORTER_ASSERT(reporter, a == b);
 }
 
 static void compare_dump(skiatest::Reporter* reporter, const SkPath& path, bool force,
         bool dumpAsHex, const char* str) {
     SkDynamicMemoryWStream wStream;
     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) {
     SkPath p;
     compare_dump(reporter, p, false, false, "");
     compare_dump(reporter, p, true, false, "");
     p.moveTo(1, 2);
     p.lineTo(3, 4);
     compare_dump(reporter, p, false, false, "path.moveTo(1, 2);\n"
                                             "path.lineTo(3, 4);\n");
@@ skipping 174 matching lines @@
     test_addEmptyPath(reporter, SkPath::kExtend_AddPathMode);
     test_addEmptyPath(reporter, SkPath::kAppend_AddPathMode);
     test_conicTo_special_case(reporter);
     test_get_point(reporter);
     test_contains(reporter);
     PathTest_Private::TestPathTo(reporter);
     PathRefTest_Private::TestPathRef(reporter);
     test_dump(reporter);
     test_path_crbugskia2820(reporter);
 }