pdf export can run out of memory and not return

Exporting a large space to pdf fails with an out of memory error. Possibly it would succeed with more memory allocated, but that's not entirely the point.

(Sub)Issues:

1. Why does it try to hold so much in memory? Why not 'stream' the space from the database into the disk?
2. When it failed, it didn't return an error message, it just left the progress bar counting up and and up and up.

Fixing either of those things would make this bug less painful.