Windows: Font with empty name string not handled.

This was uncovered while debugging QTBUG-38356 .

The attached font contains valid font data and is processed correctly on Linux, but is rejected on Windows because it's name string is empty and returning an empty string from EmbeddedFont::changeFamilyName in qtbase/src/plugins/platforms/windows/qwindowsfontdatabase.cpp is used to indicate that the change of the family name failed.

The files attached are a minimal example that tries to load the attached font (which is rejected) using QRawFont and then tries to load the arial.ttf font that is installed on windows in c:\windows\fonts\. The testfont.ttf file needs to be in the same folder as the executable.