[gtk] gl renderer: Fix color comparison

[Timm Bäder <baedert src gnome org>]

commit 2e6e6c1779edfb8359f1e65d0282e31f9fba8028
Author: Timm Bäder <mail baedert org>
Date:   Sat Dec 14 15:14:15 2019 +0100

    gl renderer: Fix color comparison

 gsk/gl/gskglrenderops.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/gsk/gl/gskglrenderops.c b/gsk/gl/gskglrenderops.c
index 84774e29aa..c2c7858dfb 100644
--- a/gsk/gl/gskglrenderops.c
+++ b/gsk/gl/gskglrenderops.c
@@ -581,7 +581,8 @@ ops_set_color (RenderOpBuilder *builder,
   ProgramState *current_program_state = get_current_program_state (builder);
   OpColor *op;
 
-  if (gdk_rgba_equal (color, &current_program_state->color))
+  if (current_program_state->color &&
+      gdk_rgba_equal (color, current_program_state->color))
     return;
 
   current_program_state->color = color;