Added code to quartz vcl implementation that takes care
when BitmapPalette.count != (depth^^2)-1 - which may
be the case anytime. If then a bitmap value exists that
goes beyond that count, a invalid access was executed

Change-Id: Iab332c91b8753aab85e9d365323f5c9e531efab2
Reviewed-on: https://gerrit.libreoffice.org/44058Reviewed-by: Bartosz Kosiorek <gang65@poczta.onet.pl>
Tested-by: Jenkins <ci@libreoffice.org>