rpcrt4: Fix memory leak of 0-byte buffer allocated during processing of bind packets.

In this case conn->server_binding will be NULL and consequently
bind->Handle will be NULL, causing I_RpcFreeBuffer to fail. Therefore
just use I_RpcFree to free the buffer as that is just what
I_RpcFreeBuffer does under the hood anyway.

dlls/rpcrt4/rpc_server.c

@@ -352,7 +352,7 @@ static void RPCRT4_process_packet(RpcConnection* conn, RpcPktHdr* hdr, RPC_MESSA
   }
 
   /* clean up */
-  I_RpcFreeBuffer(msg);
+  I_RpcFree(msg->Buffer);
   RPCRT4_FreeHeader(hdr);
   HeapFree(GetProcessHeap(), 0, msg);
 }