glx: Fix use after free in MakeCurrent

The fix from commit c468d34c - "glx: Set ContextTag for all contexts"
is actually incomplete, it correctly sets the context tag for direct
contexts as well, but would fail to mark the context's currentClient.

As a result, when the context is destroyed, it would be freed
immediately rather than being just scheduled for deletion, even though
it is still current for some client. leading to a use-after-free.

Make sure to also set the context's currentClient for direct contexts as
well, not just indirect ones.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Fixes: c468d34c - "glx: Set ContextTag for all contexts"
Closes: xorg/xserver#1186
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit aad61e8e)
3 jobs for backport-1.20-issue1186 in 6 minutes and 23 seconds (queued for 14 seconds)
Status Job ID Name Coverage
  Docker Image
passed debian-testing #11316641

00:00:29

 
  Build And Test
passed autotools-build-and-test #11316642

00:05:54

passed meson-build-and-test #11316643

00:02:49