A empty savegame slot should be emptied when it is selected

[AXDOOMER]

When there's no savegame in a slot, DoomRetro should remove the " -" when the user has pressed 'enter' on the slot. There's two spaces that a user might not see and he might let them there, so it would be better to empty the field before someone writes something.

[bradharding]

I made a change to the save game description code (commit a685216) and overlooked this instance. Will fix it shortly. Thanks.

[bradharding]

Fixed in commit 44969b0. Rather than the two spaces and hyphen being removed, they're replaced with the current map's name, as happened in previous versions.