BUG/MINOR: log: fix memory error handling in parse_logsrv()

A check was missing in parse_logsrv() to make sure that malloc-dependent
variable is checked for non-NULL before using it.

If malloc fails, the function raises an error and stops, like it's already
done at a few other places within the function.

This partially fixes GH #2130.

It should be backported to every stable versions.

src/log.c

@@ -809,6 +809,10 @@ int parse_logsrv(char **args, struct list *logsrvs, int do_del, const char *file
 			}
 
 			node = malloc(sizeof(*node));
+			if (!node) {
+				memprintf(err, "out of memory error");
+				goto error;
+			}
 			memcpy(node, logsrv, sizeof(struct logsrv));
 			node->ref = logsrv;
 			LIST_INIT(&node->list);