vlib: fix coverity 274744

Add a missing null check

Type: fix
Change-Id: Id1b27341480c9d62185496ae1d832360119ec198
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/src/vlibapi/api_shared.c b/src/vlibapi/api_shared.c
index 98da604..73ef3ce 100644
--- a/src/vlibapi/api_shared.c
+++ b/src/vlibapi/api_shared.c
@@ -232,7 +232,10 @@
   u16 id = clib_net_to_host_u16 (*((u16 *) msg));
   vl_api_msg_data_t *m = vl_api_get_msg_data (am, id);
 
-  m->endian_handler (tmpmem);
+  if (m && m->endian_handler)
+    {
+      m->endian_handler (tmpmem);
+    }
 
   if (m && m->tojson_handler)
     {