fm2 movies for FDS games cause an IndexOutOfRangeException

[TakuikaNinja]

Summary

Attempting to play an FDS movie converted from fm2 files (drag & drop/import movie) causes an IndexOutOfRangeException. From what I can tell in the source code, this functionality does not appear to be finished.

Repro

1. Start an FDS game. (games tried: SMB2J, Tonkachi Mario)
2. Drag and drop an fm2 file, or import it and then play the converted movie file.
3. "Fatal Error: IndexOutOfRangeException" window appears

Output

Host env.

• BizHawk 2.9, Linux (EndeavourOS)

[YoshiRulz]

Full stacktrace when importing https://tasvideos.org/3348M (taken on ebe3cad66):

System.IndexOutOfRangeException: Index was outside the bounds of the array.
  at BizHawk.Client.Common.Bk2Controller.SetFromMnemonic (System.String mnemonic) [0x0005b] in <973fb7a12a68494182a2aa93dd31a9ec>:0 
  at BizHawk.Client.Common.Bk2Movie.GetInputState (System.Int32 frame) [0x0007a] in <973fb7a12a68494182a2aa93dd31a9ec>:0 
  at BizHawk.Client.Common.MovieSession.LatchInputToLog () [0x00017] in <973fb7a12a68494182a2aa93dd31a9ec>:0 
  at BizHawk.Client.Common.MovieSession.HandleFrameBefore () [0x00082] in <973fb7a12a68494182a2aa93dd31a9ec>:0 
  at BizHawk.Client.EmuHawk.MainForm.StepRunLoop_Core (System.Boolean force) [0x0034d] in <4ecfa9309b57435ebe194da8a64e8a1d>:0 
  at BizHawk.Client.EmuHawk.MainForm.ProgramRunLoop () [0x001e7] in <4ecfa9309b57435ebe194da8a64e8a1d>:0 
  at (wrapper remoting-invoke-with-check) BizHawk.Client.EmuHawk.MainForm.ProgramRunLoop()
  at BizHawk.Client.EmuHawk.Program.SubMain (System.String[] args) [0x003dd] in <4ecfa9309b57435ebe194da8a64e8a1d>:0