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

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.

(cherry picked from commit b6864a5b6fa1ea6eb224710d00c897105b9e2a46)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit e10a8f6b9c9437efe8b78239c92ed18775353d1c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>