[FIXED] Upgrading a facility doesn't account for refunds

[Delian]

If you have 100k and you try to build something that costs 150k, you'll get an error, even though the building you're constructing over would refund >50k.

[Meridian]

Fixed: https://github.com/MeridianOXC/OpenXcom/commit/1b211f58d92ae2258708d1aab60323a231b84992