### Please describe the problem.

The file `Kontoauszug 01.01.2019 - 31.12.2019 - CH1234567890123456789 - 2019-12-31.pdf` can not be exported. The error message is just "failed".

I added code (pull request underway) to log IOExceptions and saw this exception message:

    /media/thk/thk-sg2/annex-exporttree-sg2/shared/finance/taxes/2019/: openTempFile: invalid argument (Invalid argument)

After renaming the file to `Kontoauszug 01012019 - 31122019 - CH2480808009412070498 - 2019-12-31.pdf` it could be exported.

I am not yet sure what exact combinations of dots, spaces and maybe dashes cause the failure.

### What version of git-annex are you using? On what operating system?

git-annex version: 8.20200309-05df404212, Debian testing
