[gnome-builder] style-scheme: allow NULL style scheme

[Christian Hergert <chergert src gnome org>]

commit e9938dffd9200ee025ff5693c0956c099b611fa2
Author: Christian Hergert <chergert redhat com>
Date:   Sun Jul 16 18:45:36 2017 -0700

    style-scheme: allow NULL style scheme
    
    This makes it easy to clear settings.

 libide/sourceview/ide-source-style-scheme.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/libide/sourceview/ide-source-style-scheme.c b/libide/sourceview/ide-source-style-scheme.c
index c188caf..dcfef6e 100644
--- a/libide/sourceview/ide-source-style-scheme.c
+++ b/libide/sourceview/ide-source-style-scheme.c
@@ -41,7 +41,7 @@ ide_source_style_scheme_apply_style (GtkSourceStyleScheme *style_scheme,
   gboolean italic = FALSE;
   gboolean italic_set = FALSE;
 
-  g_return_val_if_fail (GTK_SOURCE_IS_STYLE_SCHEME (style_scheme), FALSE);
+  g_return_val_if_fail (!style_scheme || GTK_SOURCE_IS_STYLE_SCHEME (style_scheme), FALSE);
   g_return_val_if_fail (style_name != NULL, FALSE);
 
   g_object_set (tag,
@@ -53,6 +53,9 @@ ide_source_style_scheme_apply_style (GtkSourceStyleScheme *style_scheme,
                 "style-set", FALSE,
                 NULL);
 
+  if (style_scheme == NULL)
+    return FALSE;
+
   style = gtk_source_style_scheme_get_style (style_scheme, style_name);
 
   if (style == NULL && (colon = strchr (style_name, ':')))