Fix crash in `haddock-library` on unicode space

Our quickcheck tests for `haddock-library` stumbled across an edge case
input that was causing Haddock to crash: it was a unicode space
character.

The root cause of the crash is that we were implicitly assuming that
if a space character was not " \t\f\v\r", it would have to be "\n".
We fix this by instead defining horizontal space as: any space character
that is not '\n'.

Fixes #1142

0 files changed, 0 insertions, 0 deletions