Move the cursor down
amount is greater than the maximum move distance then it is internally adjusted to the maximum. This sequence will not scroll the screen or scroll region. If
amount is 0, adjust it to 1.
This unsets the pending wrap state without wrapping.
If the current scroll region is set and the cursor is on or above bottom-most line of it then the cursor may move down only until it reaches the bottom-most line of current scroll region.
If the current scroll region is not set or the cursor is below bottom-most line of current scroll region it may move down until the bottom of the screen.
amount = 0, is not adjusted to 1.
If the cursor is below bottom-most line of current scroll region it is moved to the bottom-most line of the scroll region.