[gtksourceview/gnome-3-24] regex: fix potential use of -1 as byte offset

[Christian Hergert <chergert src gnome org>]

commit 23bc81adf6c98f76cc4afb23688bc2397ed0e948
Author: Christian Hergert <chergert redhat com>
Date:   Thu Dec 6 12:55:52 2018 -0800

    regex: fix potential use of -1 as byte offset
    
    g_match_info_pos() can return TRUE even if there was not a match, and the
    start/end position are set to -1.
    
    See g_match_info_fetch_pos() documentation for more information. This fixes
    an invalid read warning by -1 in valgrind.

 gtksourceview/gtksourceregex.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/gtksourceview/gtksourceregex.c b/gtksourceview/gtksourceregex.c
index 3934d199..7d53ceaf 100644
--- a/gtksourceview/gtksourceregex.c
+++ b/gtksourceview/gtksourceregex.c
@@ -334,7 +334,9 @@ _gtk_source_regex_fetch_pos (GtkSourceRegex *regex,
 
        g_assert (regex->resolved);
 
-       if (!g_match_info_fetch_pos (regex->u.regex.match, num, &byte_start_pos, &byte_end_pos))
+       /* g_match_info_fetch_pos() can return TRUE with start_pos/end_pos set to -1 */
+       if (!g_match_info_fetch_pos (regex->u.regex.match, num, &byte_start_pos, &byte_end_pos) ||
+           byte_start_pos == -1 || byte_end_pos == 1)
        {
                if (start_pos != NULL)
                        *start_pos = -1;