Before commit 9f3e5fe8d (Fix the way the .disk/mkisofs file is created)
all these commands (`mkdir`, write to `binary/.disk/mkisofs` and
`xorriso`) were in the same `binary.sh` script. Since that commit, the
write was extracted, to prevent issues with quoting, but the related
mkdir was left in `binary.sh`. This means that the write is now executed
first, and the `mkdir` only afterwards, making the `mkdir` quite pointless.
In practice, this did not break becaue binary_disk also does the same
`mkdir` and runs before `binary_iso`, but if one runs commands manually
and skips `binary_iso`, then this does break.
Even though this is not really a supported usecase, just move the mkdir
outside of `binary.sh`, so it runs *before* the write again as intended.
e772dfd6d2