not a fix, but a workaround for problem with Umlauten in OC6RC4

this one fixes core issue https://github.com/owncloud/core/issues/6273.
Of course it's not meant as a real fix, but as something that has to be implemented the right way. I'm not so much in the code, that I can do it myself within a reasonable time, so I guess some of the core developer can do it much faster.