BUG/MINOR: http: Missing calloc return value check while parsing redirect rule

A memory allocation failure happening in http_parse_redirect_rule when
trying to allocate a redirect_rule structure would have resulted in a
crash. This function is only called during configuration parsing.

It was raised in GitHub issue #1233.
It could be backported to all stable branches.

src/http_rules.c

@@ -408,6 +408,10 @@ struct redirect_rule *http_parse_redirect_rule(const char *file, int linenum, st
 	}
 
 	rule = calloc(1, sizeof(*rule));
+	if (!rule) {
+		memprintf(errmsg, "parsing [%s:%d]: out of memory.", file, linenum);
+		return NULL;
+	}
 	rule->cond = cond;
 	LIST_INIT(&rule->rdr_fmt);