Avoid memset(NULL, ...).

samples/shell.cc

Index: samples/shell.cc
diff --git a/samples/shell.cc b/samples/shell.cc
index e9f99896e9c3ada9afdbfa263cd0c419e54ee88f..aebe49d49e7763038bb840e93bc3d5a290a43de8 100644
--- a/samples/shell.cc
+++ b/samples/shell.cc
@@ -68,7 +68,8 @@ static bool run_shell;
 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); }