handle null vertex or index buffers in batch

src/gpu/effects/GrDashingEffect.cpp

Index: src/gpu/effects/GrDashingEffect.cpp
diff --git a/src/gpu/effects/GrDashingEffect.cpp b/src/gpu/effects/GrDashingEffect.cpp
index fc3fc670ff018ae42fa41ceb4ef026ad3241bf15..eb0467cef41d669a7b1f59e0cc8a1e988afc0dbb 100644
--- a/src/gpu/effects/GrDashingEffect.cpp
+++ b/src/gpu/effects/GrDashingEffect.cpp
@@ -536,6 +536,11 @@ public:
                                                               &vertexBuffer,
                                                               &firstVertex);
 
+        if (!vertices || !batchTarget->quadIndexBuffer()) {
+            SkDebugf("Could not allocate buffers\n");
+            return;
+        }
+
         int curVIdx = 0;
         int rectIndex = 0;
         for (int i = 0; i < instanceCount; i++) {