save/load cycle changes boardfilename

When I start new game via game menu, lets say 'L.A.MELTDOWN' episode, boardfilename[0]=='\0'. After I save and load game 'boardfilename' becomes "/E1L1.map"

I think that this may be result of 5e556269 and subsequent commits, and I consider this behavior undesirable. 'boardfilename' is used in various tests for example in 'G_HaveUserMap'. This can cause certain mods that contain more than 7 levels in first episode (Blast Radius) to end prematurely, because engine, based on if level was loaded from savefile or not, evaluates that user map, instead of episode is being played.