BUG/MINOR: ssl/ckch: always free() the previous entry during parsing

The ckch_conf_parse() function is the generic function which parses
crt-store keywords from the crt-store section, and also from a crt-list.

When having multiple time the same keyword, a leak of the previous value
happens. This patch ensure that the previous value is always freed
before overwriting it.

This patch should be backported as far as 3.0.

src/ssl_ckch.c

@@ -4870,6 +4870,7 @@ int ckch_conf_parse(char **args, int cur_arg, struct ckch_conf *f, int *found, c
 			if (ckch_conf_kws[i].type == PARSE_TYPE_STR) {
 				char **t = target;
 
+				ha_free(t);
 				*t = strdup(args[cur_arg + 1]);
 				if (!*t) {
 					ha_alert("parsing [%s:%d]: out of memory.\n", file, linenum);