Make sure not to move the caret in the wrong direction when restoring
the visual line X offset, in case the visual and logical order is
slightly different.

The algorithm used to move the cursor on the next line and restore the
X position across lines works as follows:

1. Move `cursor_offset` to the next line by incrementing it until
   reaching a line break;
2. Find the Y coordinate corresponding to the new cursor_offset;
3. Find the text closest to the new Y coordinate and the previous X
   coordinate.
4. Move cursor_offset to the text at this new (X, Y) location.

The issue lies in step 3, which can find a position on a different line
than expected in case several lines have a nearly the same Y position.

Closes #889.