egl/glx/sw: Check xcb_query_extension_reply return value for MIT-SHM

For consistency with other xcb_query_extension_reply callers.

v2:
* Now with less use-after-free. (Eric Engestrom)

Reviewed-by: Eric Engestrom <None>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33400>
2 files changed