garray: Rewrite binary search calculation to avoid integer overflow

If `right` and `left` are both near `G_MAXUINT`, it’s possible for the
addition to overflow, even if the eventual result would fit in a
`guint`. Avoid that by operating on the difference instead.

The difference is guaranteed to be positive due to the prior `left <=
right` check.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

glib/garray.c

@@ -845,7 +845,7 @@ g_array_binary_search (GArray        *array,
 
       while (left <= right)
         {
-          middle = (left + right) / 2;
+          middle = left + (right - left) / 2;
 
           val = compare_func (_array->data + (_array->elt_size * middle), target);
           if (val < 0)