rem: WMReplaceInArray(WMArray *array, unsigned index, void *item)
add: WMReplaceInArray(WMArray *array, int index, void *item)
context: WMReplaceInArray(WMArray *array, unsigned index, void *item){    void *old;    wassertrv(index > array->itemCount, 0);    if (index == array->itemCount) {        WMAddToArray(array, item);        return NULL;    }    old = array->items[index];    array->items[index] = item;    return old;}