[gtk/wip/chergert/glproto] always setup initial framebuffer

[Christian Hergert <chergert src gnome org>]

commit bc6cfedf30c83c0c27fc131137f5b74d09584bf1
Author: Christian Hergert <chergert redhat com>
Date:   Mon Feb 1 22:53:28 2021 -0800

    always setup initial framebuffer
    
    this ensures we draw the intial background just like the gl renderer
    does when doing ./tests/showrendernode

 gsk/next/gskglcommandqueue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gsk/next/gskglcommandqueue.c b/gsk/next/gskglcommandqueue.c
index 19cbc5dd0d..78121c6048 100644
--- a/gsk/next/gskglcommandqueue.c
+++ b/gsk/next/gskglcommandqueue.c
@@ -922,7 +922,7 @@ gsk_gl_command_queue_execute (GskGLCommandQueue    *self,
                               const cairo_region_t *scissor)
 {
   cairo_rectangle_int_t scissor_rect;
-  GLuint framebuffer = 0;
+  int framebuffer = -1;
   GLuint vao_id;
   int next_batch_index;
   guint program = 0;