BUG/MINOR: tools: ha_freearray() must also free the array

BUG/MINOR: tools: ha_freearray() must also free the array

ha_freearray() frees each string of a NULL-terminated array and then
sets the array pointer to NULL, but never frees the array itself.

Its only caller is ckch_conf_parse(), which uses it to release the
previous value when a PARSE_TYPE_ARRAY_SUBSTR keyword ("domains", "ips")
is specified twice on the same line, as in:

    crt-store s
      load crt site.pem domains "a.example,b.example" domains "c.example"

The strings are freed but the array of the first value is leaked
(24 bytes here, reported by LeakSanitizer with "haproxy -c -d" on a
build with -fsanitize=address). The leak only happens when parsing a
line with a duplicated keyword, which also emits an "already specified,
overwriting" warning, so the impact is minimal.

Fix it by freeing the array with ha_free(), which also sets the pointer
to NULL as before. With the patch, the same configuration with either
"domains" or "ips" repeated reports no leak.

Also accept a NULL array argument without dereferencing it. An argument
pointing to a NULL array remains safe, and non-NULL arrays are still fully
freed and their pointer cleared.

Fixes issue #3569.

This was introduced by commit 96b1f1fd2 ("MINOR: tools: ha_freearray()
frees an array of string") together with its use in commit 9c0c05b7b
("BUG/MINOR: ssl/ckch: always ha_freearray() the previous entry during
parsing"), both in 3.2-dev16, so this must be backported to 3.2.