[vte/wip/sixels] sixel: Fix broken transparency

[Hans Petter Jansson <hansp src gnome org>]

commit 9b117c0ca927ee45cdded15c20b29e44d55a3025
Author: Hans Petter Jansson <hpj hpjansson org>
Date:   Mon Nov 2 03:39:35 2020 +0100

    sixel: Fix broken transparency
    
    A missing call to param_to_color_register() caused the color index used for
    transparency to always be replaced with the background color.

 src/sixel-context.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/sixel-context.cc b/src/sixel-context.cc
index 7bfaeebe..4db40cd7 100644
--- a/src/sixel-context.cc
+++ b/src/sixel-context.cc
@@ -316,7 +316,7 @@ Context::prepare(uint32_t introducer,
                 reset_colors();
 
         /* FIXMEchpe: this all seems bogus. */
-        set_color(0, make_color(bg_red, bg_green, bg_blue));
+        set_color(param_to_color_register(0), make_color(bg_red, bg_green, bg_blue));
         if (private_color_registers)
                 set_color(param_to_color_register(0),
                           make_color(fg_red, fg_green, fg_blue));