r600g: Drop references to destroyed blend state

Fixes use-after-free when the currently bound blend state is destroyed.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85267
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84140

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>

Cc: mesa-stable@lists.freedesktop.org
diff --git a/src/gallium/drivers/r600/r600_state_common.c b/src/gallium/drivers/r600/r600_state_common.c
index 68365f9..879ec35 100644
--- a/src/gallium/drivers/r600/r600_state_common.c
+++ b/src/gallium/drivers/r600/r600_state_common.c
@@ -158,8 +158,10 @@
 	struct r600_context *rctx = (struct r600_context *)ctx;
 	struct r600_blend_state *blend = (struct r600_blend_state *)state;
 
-	if (blend == NULL)
+	if (blend == NULL) {
+		r600_set_cso_state_with_cb(&rctx->blend_state, NULL, NULL);
 		return;
+	}
 
 	r600_bind_blend_state_internal(rctx, blend, rctx->force_blend_disable);
 }
@@ -447,8 +449,13 @@
 
 static void r600_delete_blend_state(struct pipe_context *ctx, void *state)
 {
+	struct r600_context *rctx = (struct r600_context *)ctx;
 	struct r600_blend_state *blend = (struct r600_blend_state*)state;
 
+	if (rctx->blend_state.cso == state) {
+		ctx->bind_blend_state(ctx, NULL);
+	}
+
 	r600_release_command_buffer(&blend->buffer);
 	r600_release_command_buffer(&blend->buffer_no_blend);
 	FREE(blend);