index out of range after failed undo with multiple cursors

[dermetfan]

Description of the problem or steps to reproduce

As you can see, undo cleared the buffer. Micro crashed on the next character I typed.

To reproduce you need to follow the example exactly. If I jump more with the cursor, the behavior changes:

Specifications

Commit hash: v1.3.1
OS: NixOS
Terminal: lilyterm