#297 MIDI: enforce a minimum sysex delay in delaysysex

[Misty De Meo]

The current version of the delaysysex MIDI option, added in https://sourceforge.net/p/dosbox/patches/241/, doesn't enforce a minimum sysex delay. It's still possible for sysex transfers to happen too frequently for a real rev. 0 MT-32. This patch updates it to set a 40ms delay as a minimum if the calculated delay would have been shorter than that. As mentioned in the other ticket, 40ms is the number used by ScummVM and there's a few reasons to adopt it.

I tested this with MEdit, a music tracker/player designed for LAPC-I/CM-32L. Songs that would reliably trigger a buffer overflow on a real rev. 0 MT-32 now work perfectly with this patch.