MINOR: memory: also poison the area on freeing

Doing so sometimes helps detect some UAF situations without the overhead
associated to the DEBUG_UAF define.

(cherry picked from commit da52035a45d80485ca32a0b81651bba28cf00889)
[wt: will be helpful in bug reports]
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed