Oliver Sander authored Sep 27, 2018 and Albert Astals Cid committed Sep 27, 2018

If a FreeText annotation misses an AP entry, try to create a temporary font
as defined by its default appearance string. Tf operator names the font resource,
and we can search for the resource inside the default resource dictionary.
See ISO32000 sections about "Free Text Annotations" and "Variable Text".

If lookup fails for some reason, use Helvetica as fallback.

Patch done together with Tobias Deiminger