Don't mangel 8.3-filenames with chars > 0x7f

Don't mangel 8.3-filenames with chars > 0x7f

Windows produces 8.3filenames wit chars > 0x7f. Those have been rejected
by Marlin until now.

With these 'malformed' filenames can now be worked with:
In the LCD menue
With RepetierHost (V1.6.1 tested) - full support. Characters are
displayed as '?'
With Octoprint (1.2.10 tested) the files do not appear in the files
area. At the console, listed with M20 they appear with a '�'.
With Pronterface the files appear in the sd-window but you can't start
them. They are mangled by pronterface. The names are altered and than
recected by Marlin. In the console they apper with differen but not the
correct characters.

All in all a little step forward.

Fix for #3593