[PATCH] debuginfod: Clear and reset debuginfod_client winning_headers on reuse

[Frank Ch. Eigler]

Hi -

> gcc address sanitizer detected a leak of the debuginfod_client
> winning_headers when the handle was reused. Make sure to free and
> reset the winning_headers field before reuse.

This is good.

(Note we're not actually using these winning_headers bits for
anything.  That was to be part of the "return headers to application"
work whose API we were discussing under PR28284.  I suspect it'll come
to a more thorough motivation & understanding when we try to work out
PR28204 - passing file signatures).

- FChE