stats: check if stats vector entry is empty

When a stats entry is removed it is marked empty.
The stats client did not check for that and returned an empty string.
This resulted in blank lines in vpp_get_stats. Fix by returning null instead
and checking value.

Type: fix
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I08a39ba3ef4421bf275747a6300f97fe36791b50

src/vpp/app/vpp_get_stats.c

@@ -179,6 +179,8 @@ reconnect:
       for (i = 0; i < vec_len (dir); i++)
 	{
 	  char *n = stat_segment_index_to_name (dir[i]);
+	  if (!n)
+	    continue;
 	  printf ("%s\n", n);
 	  free (n);
 	}