Fix unit tests when workarounds are enabled

Change-Id: Ia660a6d91aa3615e0fa21fba67f5029c131b1ba2
Reviewed-on: https://skia-review.googlesource.com/128983
Commit-Queue: Adrienne Walker <enne@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/gl/GrGLCreateNullInterface.cpp b/src/gpu/gl/GrGLCreateNullInterface.cpp
index 3b8b1fe..9df2265 100644
--- a/src/gpu/gl/GrGLCreateNullInterface.cpp
+++ b/src/gpu/gl/GrGLCreateNullInterface.cpp
@@ -403,6 +403,9 @@
         Framebuffer* framebuffer = fFramebufferManager.lookUp(id);
 
         GrAlwaysAssert(GR_GL_RENDERBUFFER == renderbuffertarget);
+        if (!renderBufferID && !fCurrRenderbuffer) {
+           return;
+        }
         GrAlwaysAssert(fCurrRenderbuffer);
         Renderbuffer* renderbuffer = fRenderbufferManager.lookUp(fCurrRenderbuffer);