Bug#639614: empty outline titles

[Sune Stolborg Vuorela]

Control: forwarded -1 https://gitlab.freedesktop.org/poppler/poppler/-/merge_requests/1427
Control: tags -1 +patch

A patch submitted upstream.
-- 
I didn’t stop pretending when I became an adult, it’s just that when I was a 
kid I was pretending that I fit into the rules and structures of this world. 
And now that I’m an adult, I pretend that those rules and structures exist.
   - zefrank