Fix DeferredTextureImage test on Mac

Change-Id: I34cf12b2aa16b2441b9e57162cbaee1444f42c52
Reviewed-on: https://skia-review.googlesource.com/29607
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/tests/ProxyTest.cpp b/tests/ProxyTest.cpp
index 547d3b2..a9b4643 100644
--- a/tests/ProxyTest.cpp
+++ b/tests/ProxyTest.cpp
@@ -251,6 +251,9 @@
                     if (renderable) {
                         desc.fFlags = kRenderTarget_GrSurfaceFlag;
                         tex = provider->createTexture(desc, budgeted);
+                        if (!tex) {
+                            continue; // This can fail on Mesa
+                        }
                         sk_sp<GrRenderTarget> rt(sk_ref_sp(tex->asRenderTarget()));
 
                         sk_sp<GrSurfaceProxy> sProxy(GrSurfaceProxy::MakeWrapped(rt, origin));