Cold boot not working if floppy in drive B

[giomba]

Steps to reproduce:

1. make sure that you are using a branch with the new reset feature (cold boot)
2. start emulator with CP/M disk in drive A:
3. do something (eg. type DIR at the CCP prompt) (optional?)
4. switch disk drive (eg. type B: at the CCP prompt)
5. the emulated software hangs (correct) waiting for a disk to be inserted in drive B:
6. CTRL+ALT+BOOT does nothing (correct, same happens on the actual machine) (just for info)
7. reset the emulation by typing reset in the emulator command line
8. sometimes, the computer is unable to boot again from drive A:, and a full emulator restart is required (eg. quit)