ofp-port: Fix null dereference parsing Intel custom statistics.

Reported-at: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9788
Fixes: 7333c3b ("ofp-port: Fix buffer overread parsing Intel custom statistics.")
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/ofp-port.c

@@ -1616,7 +1616,7 @@ parse_intel_port_custom_property(struct ofpbuf *payload,
 
         /* Counter name. */
         uint8_t *name_len = ofpbuf_try_pull(payload, sizeof *name_len);
-        char *name = ofpbuf_try_pull(payload, *name_len);
+        char *name = name_len ? ofpbuf_try_pull(payload, *name_len) : NULL;
         if (!name_len || !name) {
             return OFPERR_OFPBPC_BAD_LEN;
         }