macosx: Update error alert on Metadata update failure
macosx: Update error alert on Metadata update failure

This updates the Metadata update alert, which used the deprecated
NSRunAlertPanel function.
Removed the goto.

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc