Avoid memset(NULL, ...).

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 8ea77fdb1b9313943bdbf7f6ef99a0c6c5040291..502187a9a70d9d9437689d4c98df7104910a3666 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1450,7 +1450,8 @@ static void DumpHeapConstants(i::Isolate* isolate) {
 class ShellArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
  public:
   virtual void* Allocate(size_t length) {
-    return memset(AllocateUninitialized(length), 0, length);
+    void* data = AllocateUninitialized(length);
+    return data == NULL ? data : memset(data, 0, length);
   }
   virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
   virtual void Free(void* data, size_t) { free(data); }