[tepl] StyleSchemeChooserWidget: avoid a critical message if style scheme NULL

[Sébastien Wilmet <swilmet src gnome org>]

commit d2a6904bf89697825b15fc6f2032a1ab08aa8fcb
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Wed Apr 22 16:06:39 2020 +0200

    StyleSchemeChooserWidget: avoid a critical message if style scheme NULL

 tepl/tepl-style-scheme-chooser-widget.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/tepl/tepl-style-scheme-chooser-widget.c b/tepl/tepl-style-scheme-chooser-widget.c
index c041fc2..8f0ecfb 100644
--- a/tepl/tepl-style-scheme-chooser-widget.c
+++ b/tepl/tepl-style-scheme-chooser-widget.c
@@ -409,6 +409,10 @@ tepl_style_scheme_chooser_widget_set_style_scheme_id (TeplStyleSchemeChooserWidg
 
        manager = gtk_source_style_scheme_manager_get_default ();
        style_scheme = gtk_source_style_scheme_manager_get_scheme (manager, style_scheme_id);
-       gtk_source_style_scheme_chooser_set_style_scheme (GTK_SOURCE_STYLE_SCHEME_CHOOSER (chooser),
-                                                         style_scheme);
+
+       if (style_scheme != NULL)
+       {
+               gtk_source_style_scheme_chooser_set_style_scheme (GTK_SOURCE_STYLE_SCHEME_CHOOSER (chooser),
+                                                                 style_scheme);
+       }
 }