kvm tools: set "done" to true on SDL window close

Currently, SDL doesn't exit on window close because it stuck in sdl__stop because "done" is not set to true.

Fix it by setting "done" to true on window close.

---
 tools/kvm/ui/sdl.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index 9994490..a260002 100644
@@ -265,6 +265,7 @@ static void *sdl__thread(void *p)
 		return NULL;
 	}
 exit:
+	done = true;
 	kvm_cpu__reboot(fb->kvm);
 
 	return NULL;

1.7.2.5

Applied, thanks!