Fix exception during vertical paragraph navigation (#16276)
Closes #16274
Summary of the issue:
Exception during vertical navigation when one of page items is offscreen.
Description of user facing changes
N/A
Description of development approach
Previously I was retrieving x coordinate by calling textInfo.pointAtStart. However it appears that this doesn't work when said textInfo is off screen.
Switching to another method:
textInfo.NVDAObjectAtStart.location[0]
