bugfix in cursor positioning

bugfix in cursor positioning

scenario:
- create a long wrapping line
- tap past end of first screen line

Before this commit the cursor would be positioned not quite at the end
of the screen line but one character before. In effect there was no way
to position cursor at end of a wrapping line.

I'm not sure how this bug has lasted so long. It was introduced in
commit 8d3adfa36 back in June 2022, which was itself billed as a bugfix
for "clicking past end of screen line". But when I go back to it this
bug exists even back then. How did I miss it?! I wrote a test back then
-- and the test was wrong, has always been wrong.