[gtk/wip/otte/sortlistmodel] mergesort: Fix up an off-by-one error

[Matthias Clasen <matthiasc src gnome org>]

commit 8f71a20a7c78fe5de4e6699f85199e6687cc37e9
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jul 10 13:06:15 2020 -0400

    mergesort: Fix up an off-by-one error
    
    This makes the sort-performance test not crash.
    I have only done minimal checks that it still
    sorts correctly.

 gtk/gtksor5listmodel.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtksor5listmodel.c b/gtk/gtksor5listmodel.c
index 1111cd8777..133082240e 100644
--- a/gtk/gtksor5listmodel.c
+++ b/gtk/gtksor5listmodel.c
@@ -157,7 +157,10 @@ merge (SortArray *items,
        GtkSorter *sorter)
 {
   int start2 = mid + 1;
-  int c = 1;
+  int c = 0;
+
+  if (mid == end)
+    return 0;
 
   if (gtk_sorter_compare (sorter,
                           sort_array_get (items, mid),