Avoid rendering invisible Type3 fonts (issue 5421)

According to the PDF specification, only text rendering mode `3` (i.e. invisible) should have any effect on Type3 fonts, see http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#G8.1772271.
Hence when Type3 text is invisible, it seems that we should simply not render it.

Fixes #5421.