Before this commit, a file called `1-file.kra` would autosave
as `.-file.kra-autosave.kra`.
This commit fixes that behaviour and now it will autosave
as `.1-file.kra-autosave.kra`.

More cases:
- `1file.kra` would become `.file.kra-autosave.kra`
- `1 file.kra` would become `. file.kra-autosave.kra`
Now all of those work correctly and contain the beginning number.