Fix crash when querying a runtime config that is defined in environment

tests/UnitTestTest.cpp

Index: tests/UnitTestTest.cpp
diff --git a/tests/UnitTestTest.cpp b/tests/UnitTestTest.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e3e1b97685f63f23dff4892fe6ba0a4875d4e6f9
--- /dev/null
+++ b/tests/UnitTestTest.cpp
@@ -0,0 +1,18 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkRTConf.h"
+#include "Test.h"
+
+static void test_runUnitTests(skiatest::Reporter* reporter) {
+#ifdef SK_SUPPORT_UNITTEST
+    SkRTConfRegistry::UnitTest();
+#endif
+}
+
+#include "TestClassDef.h"
+DEFINE_TESTCLASS("UnitTest", UnitTestTestClass, test_runUnitTests)