editor: Fix cursor positioning with pointer and touch
editor: Fix cursor positioning with pointer and touch

The calculation off the vertical offset between the widget coordinates
and where the text was rendered was wrong. It was using the constant for
horizontal offset for that too.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=78411

kwm81/weston,Tarnyko/weston-xdg_surface_present,xorgy/weston,giucam/weston,udoprog/weston,udoprog/weston,giucam/weston,mchalupa/weston,Tarnyko/weston-xdg_surface_present,sir-murray/weston,Fantu/compositor-spice,krezovic/weston,Fantu/compositor-spice,krezovic/weston,Gnurou/weston,kwm81/weston,eyolfson/weston,Gnurou/weston,mchalupa/weston,Fantu/compositor-spice,sir-murray/weston,jonnylamb/weston,eyolfson/weston,jonnylamb/weston,xorgy/weston