completion menu cut when window is small

[elig0n]

When the command completion menu is shown and shrinking the window from top to bottom
the completion menu can be cut in place and the top completions may become invisible
I would expect the completion menu height to shrink proportionally with the resize once it gets
to its height and keep shown what would otherwise could be visible completion options.

Example:

i.e. there is no need for the empty space between the command line and the completion options
and it would be nice if it could grow smaller in height.