[gimp/wip/wormnest/fix-themes-windows] fix: themes_theme_change_notify: error parsing theme.css on Windows.

[Jacob Boerema <jboerema src gnome org>]

commit 14106715864a13fd5b7065670bacc6bb22c77db4
Author: Jacob Boerema <jgboerema gmail com>
Date:   Thu Sep 24 11:17:56 2020 -0400

    fix: themes_theme_change_notify: error parsing theme.css on Windows.
    
    When loading a theme on Windows we always get an error like:
    themes_theme_change_notify: error parsing [path including drive letter to:]\theme.css: 
theme.css:8:99Failed to import: Operation not supported
    
    The location points to the end of the filename of the first @ import url string.
    Investigation shows that on Windows it only gets correctly read if there
    is a file protocol attached to the start of the filename.

 app/gui/themes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/app/gui/themes.c b/app/gui/themes.c
index 065af8ad11..d2d720e690 100644
--- a/app/gui/themes.c
+++ b/app/gui/themes.c
@@ -298,7 +298,7 @@ themes_apply_theme (Gimp          *gimp,
 
               g_output_stream_printf (
                 output, NULL, NULL, &error,
-                "@import url(\"%s\");\n",
+                "@import url(\"file:///%s\");\n",
                 esc_path);
 
               g_free (esc_path);