[folks] PotentialMatch: use a correct index upper bound.

[Niels De Graef <nielsdg src gnome org>]

commit 765febf7a02adf62b01f86eb4e7dbfd548b4e99d
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Wed Jan 3 23:19:31 2018 +0100

    PotentialMatch: use a correct index upper bound.
    
    This is probably the root cause for bug 739997[1].
    
    [1]: https://bugzilla.gnome.org/show_bug.cgi?id=739997

 folks/potential-match.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/folks/potential-match.vala b/folks/potential-match.vala
index 2148269..ecaf349 100644
--- a/folks/potential-match.vala
+++ b/folks/potential-match.vala
@@ -669,7 +669,7 @@ public class Folks.PotentialMatch : Object
       if (pos < haystack_len && ch == c)
         return 0;
 
-      uint idx = ((int) pos - (int) max_dist).clamp (0, haystack_len);
+      uint idx = ((int) pos - (int) max_dist).clamp (0, haystack_len - 1);
       ch = 0;
 
       while (idx < pos + max_dist && (ch = haystack[idx]) != 0)