Up and down buttons should not move when reaching the first or last line

[herrbrixter]

Is your feature request related to a problem? Please describe.
Up and down should keep the cursor's columnar position but this doesn't happen on the first and last lines.

1. Pressing up when the cursor is on the first line would place the cursor at the start of the first line.
2. Pressing down when the cursor is on the last line would place the cursor at the end of the last line.

If there is only one line, pressing either up or down would misplace the cursor. These buttons shouldn't do anything when there are no other lines.

Describe the solution you'd like

1. Pressing up when the cursor is on the first line would not move the cursor.
2. Pressing down when the cursor is on the last line would not move the cursor.

Use case
For text formatting, if you only want to edit a certain column, the current behavior requires you to go back to the middle position because the Up and Down buttons brought the cursor to the start or end of the line.

Describe alternatives you've considered (if any)
Manually moving the cursor back to the original middle position.

[herrbrixter]

Related to #1076