Fix GLInterfaceValidation test after "Remove GrContextFactory::getGLContext"

tests/GLInterfaceValidationTest.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 "Test.h"
 
 // This is a GPU-backend specific test
 #if SK_SUPPORT_GPU
 
 #include "GrContextFactory.h"
 
 DEF_GPUTEST(GLInterfaceValidation, reporter, factory) {
     for (int i = 0; i <= GrContextFactory::kLastGLContextType; ++i) {
         GrContextFactory::GLContextType glCtxType = (GrContextFactory::GLContextType)i;
         // this forces the factory to make the context if it hasn't yet
         GrContextFactory::ContextInfo* contextInfo = factory->getContextInfo(glCtxType);
-        SkGLContext* glCtx = contextInfo->fGLContext;
+        SkGLContext* glCtx = contextInfo ? contextInfo->fGLContext : nullptr;
 
         // We're supposed to fail the NVPR context type when we the native context that does not
         // support the NVPR extension.
         if (GrContextFactory::kNVPR_GLContextType == glCtxType &&
             factory->getContextInfo(GrContextFactory::kNative_GLContextType) &&
             !factory->getContextInfo(GrContextFactory::kNative_GLContextType)->fGLContext->gl()->hasExtension("GL_NV_path_rendering")) {
             REPORTER_ASSERT(reporter, nullptr == glCtx);
             continue;
         }
 
         REPORTER_ASSERT(reporter, glCtx);
         if (glCtx) {
             const GrGLInterface* interface = glCtx->gl();
             REPORTER_ASSERT(reporter, interface->validate());
         }
     }
 }
 
 #endif