create_temp_file/gen_path: prevent memory leak if gc == NULL

create_temp_file/gen_path: prevent memory leak if gc == NULL

If gc == NULL, the data allocated in the alloc_gc_buf() call in
create_temp_file or the string_mod_const call in gen_path would never
be free'd.

These functions are currently never called that way, but let's prevent
future problems.

While touching create_temp_file, also remove the counter variable, which is
never read, simplify the do-while to a while loop, and truncate the prefix
(if needed) to preserve the random and extension of the created filename.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20171101220342.14648-5-steffan@karger.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15703.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>