[BUG] Can't schedule multiple nexp values in one line

[pgriffin17]

Describe the bug
With multiple filters, in a schedule file, like
source "NGC7331" filter red,green,blue exptime 5,10,15 readout 2 nexp 3,5,7
we cannot do differing nexp values per filter (here I'd expect it to schedule 3x5s red images, 5x10s greens, 7x15s blues). Instead this results in an error when reading in the schedule file due to the different nexp values.

To Reproduce
Steps to reproduce the behavior:

1. Create schedule with source line above
2. Run schedtel
3. Get error

Desktop (please complete the following information):
TCC1