create tape dir on record, if the user has deleted it

[catfact]

not sure if this is really desired, but:

• currently, there is a check for nil file handle to audio/tape/index.txt when reading to increment tape filename.
• however, there is no analogous check for nil when writing to the same file a few lines later.

it is possible to run into this if a user deletes their audio/ or audio/tape/. (why would they do this? don't ask me. but it happened and this burned some support time.)

so this change creates ~/dust/audio/tape/ and parents before writing the index file, if the initial attempt results in a nil handle.