Insert next unused or empty sequence wraps around at 7f

[micheldebree]

Keep pressing ctrl-f (or ctrl-shift-f in the latest code) on a000 until a07f is inserted. Press it again, now a001 is inserted again, which is in use by that time, so it shouldnt be inserted. This comes to a stop after another 7f inserts, but I suspect it's because the orderlist is full.

[Chordian]

See also issue #82 about adding a dialog box when the sequence cap has been reached.