MFDv5 with --inFrames silently ignores --fmin and --fBand

As discovered by @patrick-meyers when calling MFDv5 on input frames and giving it frequency band options, it silently ignores those and writes out SFTs over the full [0,1/fSamp] band. That's wasteful and confusing. I went through the code and think I have a safe solution, will make a MR soon.