[gitg] Fix offset from parsing tags

[Alberto Fanjul <albfan src gnome org>]

commit 2ba2cf8b683cb9de36bc47e4055bf3896d9c1c25
Author: Alberto Fanjul <albertofanjul gmail com>
Date:   Sat Jan 22 13:47:01 2022 +0100

    Fix offset from parsing tags

 libgitg/gitg-diff-view.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libgitg/gitg-diff-view.vala b/libgitg/gitg-diff-view.vala
index da37d05d..00b125ed 100644
--- a/libgitg/gitg-diff-view.vala
+++ b/libgitg/gitg-diff-view.vala
@@ -322,8 +322,8 @@ public class Gitg.DiffView : Gtk.Grid
                                int start_pos, end_pos;
                                string text = matchInfo.fetch(0);
                                matchInfo.fetch_pos (0, out start_pos, out end_pos);
-                               buffer.get_iter_at_offset(out start, start_pos);
-                               buffer.get_iter_at_offset(out end, end_pos);
+                               buffer.get_iter_at_offset(out start, start_pos -1);
+                               buffer.get_iter_at_offset(out end, end_pos -1);
 
                                var tag = buffer.create_tag(null, "underline", Pango.Underline.SINGLE);
                                tag.foreground_rgba = custom_color_link;