Fix display of VT100 vertically-offset horizontal line characters

(o,p,r,s). They are displayed in Windows by actually writing the
centred one (q) with a vertical offset, in case fonts don't have the
offset versions; this requires terminal.c to separate those characters
into distinct calls to do_text(). Unfortunately, it was only breaking
up a text-drawing call _before_ one of those characters, not after
one. Spotted by Robert de Bath.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9221 cda61777-01e9-0310-a592-d414129be87e