ZusiDisplay sometimes loads the same font file into two different PrivateFontCollections using two threads, so there is a race condition when the file is opened without the FILE_SHARE_READ sharing mode. The second call to GdipPrivateAddFontFile() might fail if the first one hasn't closed the file handle yet.
-- v2: gdiplus: Use FILE_SHARE_READ in GdipPrivateAddFontFile(). gdiplus/tests: Test for GdipPrivateAddFontFile() sharing violation.