glx: get rid of memory leak

It fixes Coverity issue: `CID 1468356:  Resource leaks  (RESOURCE_LEAK)`

Fixes: e1964496 ("glx: initial plumbing to let users force-enable/disable extensions")
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7310>
1 file changed