During a test, I needed to issue 2 "cont" commands at gdb to advance just one
frame at one breakpoint I trapped. And when closing the player, I issued twice
"cont" at gdb, and only after the segfault occured.

I suspect the function "radeon_dri2_screen_init" at "radeon_dri2.c" is called
twice, one for each Screen, and then this routine is scheduling the
"radeon_dri2_client_state_changed" routine twice with "AddCallBack".

This way, when the client state is changed to gone, the "destroy buffers"
routine is called twice either, and the error occur.

I also want to thank the devs for the radeon driver!
Thank you!