really completing 'adapt build meta data for better differentiation to 4.1'
124639: correct consideration of not provided header offset when checking certain read header data
#i124617# make CoreText tolerate PDF-export's unexpected font switches

For some documents it was observed that the PDF-export switches the font after
text layout and before text drawing/measuring. This use case is quite atrocious
and unexpected and crashed our CoreText glue code. The other platforms survive
it though; to minimize the risk to them only the CoreText glue gets adapted to
survive this scenario.