Bug found in mfm_emu

[d...@pdp8online.com]

Found problem seen in this thread

https://groups.google.com/g/mfm-discuss/c/elsfSyhYoYQ

I have released 4.20 with fix. Problem was seen with Adaptec ACB-4000 controller running long software builds. When the emulator was selected it could output data from the wrong head for a short time. This has existed since rev C board was released. I didn't see any issues with my controllers. You might want to try the new version if you have seen occasional errors from the host computer or if you have seen  glitch count messages printed by mfm_emu.