Backup command reports incorrect device for error

[fredrikr]

Test Environment (required)

• Platform: MEGA65 R3
• ROM Release: (i.e. 920413)
• Core Commit: aaf4542

Describe the bug
I had a disk in the internal drive, and I accidentally bumped the table while formatting it. I let if finish formatting, hoping it would be okay.

I then mounted a disk image as device 9, and did: BACKUP U9 TO U8

After a short while, I got a message saying "read error on device 9" (may not be the exact words).

I retried several times, and the same thing happened.

I reformatted the disk in drive 8 and tried BACKUP again, and it worked fine.

To Reproduce
Steps to reproduce the behavior:

1. Insert a disk that has sectors that are broken in device 8
2. Mount a disk image in device 9
3. BACKUP U9 TO U8
4. You should now get a message saying there's a read error on device 9, which is incorrect

Expected behavior
The read error should say device 8.

Screenshots

Additional context