radv/winsys: check more allocation failures

While we are at it, use local variables first to make sure to
not leak memory if something bad happens.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5872>
2 files changed