Mojo C++ bindings: reject messages version 2 with null payload pointer.

mojo/public/cpp/bindings/lib/message_header_validator.cc

Index: mojo/public/cpp/bindings/lib/message_header_validator.cc
diff --git a/mojo/public/cpp/bindings/lib/message_header_validator.cc b/mojo/public/cpp/bindings/lib/message_header_validator.cc
index 9f8c6278c07d0c520ad3ef11e3191d65307e4982..1f232565d4fdfb375b387869893fea97e3a1d609 100644
--- a/mojo/public/cpp/bindings/lib/message_header_validator.cc
+++ b/mojo/public/cpp/bindings/lib/message_header_validator.cc
@@ -73,9 +73,11 @@ bool IsValidMessageHeader(const internal::MessageHeader* header,
   //   payload size).
   // - Validation of the payload contents will be done separately based on the
   //   payload type.
-  if (!header_v2->payload.is_null() &&
-      (!internal::ValidatePointer(header_v2->payload, validation_context) ||
-       !validation_context->ClaimMemory(header_v2->payload.Get(), 1))) {
+  if (!internal::ValidatePointerNonNullable(header_v2->payload,
+                                            "null payload in message header",
+                                            validation_context) ||
+      !internal::ValidatePointer(header_v2->payload, validation_context) ||
+      !validation_context->ClaimMemory(header_v2->payload.Get(), 1)) {
     return false;
   }