vpkpp: V:TMB VPK load error

[craftablescience]

Btw, found issue with VPK in case there are no full numbered VPKs set in folder. If all is okay, VPKEdit load full file set - but if some pack*** nubmers are skipped, we just get view error. I'd suggest to fix it by loading the single VPK, as if there are no full set, it's supposed to be edited one by one. All VPKs are fully independent from each-other, so this would be desired behavior in that cases.

Originally posted by @Psycho-A in #220