Record fails when second, unarmed instrument is added (using multichannel card)

[Ben Webb]

Steps to reproduce:

1) Add first instrument, set to correct input, and record, this works
2) Add second instrument, and leave unarmed
2a) Optionally, set the input to something other than default (this makes no difference to the outcome)
3) Record, and watch it do the I'm-not-going-to-record-or-scroll-but-won't-tell-you-why fail
4) Stop, and get the nothing-has-been-recorded-error

If the second instrument is armed and set to a correct input, recording will happen succesfully.