Screenshots UI Code Update

The screenshots display code now works as it should.

With clones, MAMEdOX will check to see if the clone screenshot exists. if not it uses the parent screenshot.

For Example: PROGEARJ is a clone of PROGEAR. MAMEdOX checks to see if PROGEARJ.PNG exists and displays it if found. if PROGEARJ.PNG doesn't exist, MAMEdOX will display PROGEAR.PNG instead. This type of behaviour is exhibited in MAME32.

Previously, MAMEdOX would use the parent screenshot for a clone, whether a clone screenshot existed or not.

Unfortunately, this update makes the 'screenshot uses parent/clone' option (coded by HK$) obselete. Sorry about that HK$!.