mimeopen with UTF-8 characters in parent directory name

[phallobst]

As a follow-up to issue #15: If a parent directory name contains a UTF-8 character, mimeopen does not handle this properly.

> mimeopen ä/x.pdf 
Opening "�/x.pdf" with Document Viewer  (application/pdf)

So far, so good - but now for my next trick:

> cd ä
> mimeopen x.pdf 
Opening "x.pdf" with Document Viewer  (application/pdf)

** (xreader:116105): WARNING **: 15:33:57.311: Error when getting information for file “/home/ml/ä/x.pdf”: No such file or directory
[...]

Calling xreader x.pdf within that directory (or with the full path) works correctly.