glx: Initialize share_xid in CreateContext

Previously the share_xid was only set in the glXImportContextEXT path,
and it was left set to None in all of the other create-context paths.

Fixes the piglit test glx-query-context-info-ext.

NOTE: This is a candidate for the 7.11 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/glx/glxcmds.c

@@ -344,6 +344,7 @@ CreateContext(Display *dpy, int generic_id, struct glx_config *config,
    UnlockDisplay(dpy);
    SyncHandle();
 
+   gc->share_xid = shareList ? shareList->xid : None;
    gc->imported = GL_FALSE;
    gc->renderType = renderType;