gptrarray: Correctly set copied array length in g_ptr_array_copy()

The allocation size was set correctly before, but not the array length,
so the copied array appeared to have zero elements.

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

glib/garray.c

@@ -1051,6 +1051,8 @@ g_ptr_array_copy (GPtrArray *array,
               array->len * sizeof (*array->pdata));
     }
 
+  new_array->len = array->len;
+
   return new_array;
 }