[gtksourceview] vim: add support for :set syntax=off

[Christian Hergert <chergert src gnome org>]

commit b0b889573ca1eb4f903ac08e554153f048bb1bb6
Author: Christian Hergert <chergert redhat com>
Date:   Fri Jan 28 14:22:08 2022 -0800

    vim: add support for :set syntax=off

 gtksourceview/vim/gtksourcevimcommand.c | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/gtksourceview/vim/gtksourcevimcommand.c b/gtksourceview/vim/gtksourcevimcommand.c
index 5540da48..dc01d3c1 100644
--- a/gtksourceview/vim/gtksourcevimcommand.c
+++ b/gtksourceview/vim/gtksourcevimcommand.c
@@ -1205,6 +1205,11 @@ gtk_source_vim_command_set (GtkSourceVimCommand *self)
                        language = gtk_source_language_manager_get_language (manager, ft);
 
                        gtk_source_buffer_set_language (buffer, language);
+
+                       if (language != NULL)
+                       {
+                               gtk_source_buffer_set_highlight_syntax (buffer, TRUE);
+                       }
                }
                else if (g_str_has_prefix (part, "ts=") ||
                         g_str_has_prefix (part, "tabstop="))
@@ -1242,6 +1247,10 @@ gtk_source_vim_command_set (GtkSourceVimCommand *self)
                                        gtk_source_view_set_right_margin_position (view, n);
                        }
                }
+               else if (g_str_equal (part, "syntax=off"))
+               {
+                       gtk_source_buffer_set_highlight_syntax (buffer, FALSE);
+               }
                else if (g_str_equal (part, "et") ||
                         g_str_equal (part, "expandtab"))
                {