BUG/MINOR: http: Missing calloc return value check in make_arg_list

BUG/MINOR: http: Missing calloc return value check in make_arg_list

A memory allocation failure happening in make_arg_list when trying to
allocate the argument list 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 17acbab0ac5933205788eb0a134f9e918247efef)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 6d303d66057957dead2b26e8cd865cd30054902d)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>