[gtksourceview] contextengine: check for BOM when checking first_line

[Christian Hergert <chergert src gnome org>]

commit 06ad24c56d602acee12ae250dcea9b469249a083
Author: Christian Hergert <chergert redhat com>
Date:   Tue Dec 1 13:47:34 2020 -0800

    contextengine: check for BOM when checking first_line
    
    This is needed so that we do not check 0==1 when we had a BOM that was
    found in the first line (and therefore start_offset will be 1).
    
    Fixes #168

 gtksourceview/gtksourcecontextengine.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtksourceview/gtksourcecontextengine.c b/gtksourceview/gtksourcecontextengine.c
index 6ce3a5ad..a970d793 100644
--- a/gtksourceview/gtksourcecontextengine.c
+++ b/gtksourceview/gtksourcecontextengine.c
@@ -5533,7 +5533,7 @@ update_syntax (GtkSourceContextEngine *ce,
                        line_end_offset = gtk_text_iter_get_offset (&line_end);
                }
 
-               first_line = start_offset == line_start_offset;
+               first_line = (start_offset - had_bom) == line_start_offset;
        }
 
        if (analyzed_end == gtk_text_buffer_get_char_count (buffer))