handle null vertex or index buffers in batch

gm/beziereffects.cpp

Index: gm/beziereffects.cpp
diff --git a/gm/beziereffects.cpp b/gm/beziereffects.cpp
index 45c6341848ee09e73f8103a3e31c9203e8da9dc8..d86a8b8163ace9eff83a5fd1df320ba361d719da 100644
--- a/gm/beziereffects.cpp
+++ b/gm/beziereffects.cpp
@@ -76,6 +76,11 @@ private:
                                                               &vertexBuffer,
                                                               &firstVertex);
 
+        if (!vertices || !batchTarget->quadIndexBuffer()) {
+            SkDebugf("Could not allocate buffers\n");
+            return;
+        }
+
         SkASSERT(vertexStride == sizeof(Vertex));
         Vertex* verts = reinterpret_cast<Vertex*>(vertices);
 
@@ -478,6 +483,11 @@ private:
                                                               &vertexBuffer,
                                                               &firstVertex);
 
+        if (!vertices || !batchTarget->quadIndexBuffer()) {
+            SkDebugf("Could not allocate buffers\n");
+            return;
+        }
+
         SkASSERT(vertexStride == sizeof(Vertex));
         Vertex* verts = reinterpret_cast<Vertex*>(vertices);