glx: Don't use current context in __glXSendError

glx: Don't use current context in __glXSendError

There's no guarantee that there is one, and we don't need one anyway.

Fixes piglit tests:

glx@glx-fbconfig-bad
glx@glx_ext_import_context@import context, multi process
glx@glx_ext_import_context@import context, single process

Fixes: 2e3f067458e4 ("glx: fix error code when there is no context bound")
Cc: "11.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>