nouveau: there may not have been a texture if the fbo was incomplete

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Cc: "10.0 10.1" <mesa-stable@lists.freedesktop.org>

src/mesa/drivers/dri/nouveau/nouveau_fbo.c

@@ -265,7 +265,8 @@ static void
 nouveau_finish_render_texture(struct gl_context *ctx,
 			      struct gl_renderbuffer *rb)
 {
-	texture_dirty(rb->TexImage->TexObject);
+	if (rb && rb->TexImage)
+		texture_dirty(rb->TexImage->TexObject);
 }
 
 static int