Med: list_ticket: fix a memleak in case of buffer too small

Note that such a case seems impossible but there may be other issues
that will add up (see, e.g., reckless snprintf use pointed out with
ClusterLabs/pacemaker#810, something should
eventually be reflected here as well).

Discovered-by: static analysis/Coverity

src/ticket.c

@@ -410,8 +410,10 @@ int list_ticket(char **pdata, unsigned int *len)
 			cp += snprintf(cp, alloc - (cp - data), "\n");
 		}
 
-		if (alloc - (cp - data) <= 0)
+		if (alloc - (cp - data) <= 0) {
+			free(data);
 			return -ENOMEM;
+		}
 	}
 
 	*pdata = data;