[gtksourceview] contextengine: clear invalid ranges if BOM is found

[Christian Hergert <chergert src gnome org>]

commit 54e48e9c45e0ccef4d8fd8f5b9a8660aa6b0ae0b
Author: Christian Hergert <chergert redhat com>
Date:   Sat Apr 20 16:52:04 2019 -0700

    contextengine: clear invalid ranges if BOM is found
    
    If we came across a BOM at the beginning of a buffer, then we will have
    an invalid range before we check for BOM. In that case, we need to to
    clear it before we proceed or some assertions (such as invalid range == 1)
    will not be met.
    
    Fixes #30

 gtksourceview/gtksourcecontextengine.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtksourceview/gtksourcecontextengine.c b/gtksourceview/gtksourcecontextengine.c
index 9b34c72f..13554f8f 100644
--- a/gtksourceview/gtksourcecontextengine.c
+++ b/gtksourceview/gtksourcecontextengine.c
@@ -5389,6 +5389,8 @@ update_syntax (GtkSourceContextEngine *ce,
                {
                        gtk_text_iter_forward_char (&start_iter);
                        start_offset = gtk_text_iter_get_offset (&start_iter);
+                       segment_remove (ce, invalid);
+                       CHECK_TREE (ce);
                }
        }