Avoid messing up the display when too many letters are guessed at once.

Avoid messing up the display when too many letters are guessed at once.

The field to put them in was made 26 characters wide... but includes
the string "Guessed: ". So if you get to 17 it wraps to the next line
and clreol()'s it. Instead, when reaching this point step on the
"Guessed:" string instead.

Reported by phil@.