BUG/MEDIUM: httpclient/lua: double LIST_DELETE on end of lua task

BUG/MEDIUM: httpclient/lua: double LIST_DELETE on end of lua task

The lua httpclient cleanup can be called in 2 places, the
hlua_httpclient_gc() and the hlua_httpclient_destroy_all().

A LIST_DELETE() is performed to remove the hlua_hc struct of the list.
However, when the lua task ends and call hlua_ctx_destroy(), it does a
LIST_DELETE() first, and then the gc tries to do a LIST_DELETE() again
in hlua_httpclient_gc(), provoking a crash.

This patch fixes the issue by doing a LIST_DEL_INIT() instead of
LIST_DELETE() in both cases.

Should fix issue #1958.

Must be backported where bb58142 is backported.