fix middlemouse-hold-overlay-menu height

[dieterdreist]

Currently for ways which are part of several relations with many tags, I cannot see the bottom of the window because it is offscreen below. For longer lists that still fit on the screen, I have to move the object to the top of the window so the end is visible.

See screenshot

I believe the window height for the overlay is not calculated correctly. It should be avoided to have the lower edge of the overlay offscreen (also because it is not moving with the map so it will remain hidden if you drag up), currently it assumes it can take up to the full window height before it will become scrollable (and also then you cannot see the very end of the list because a bit is missing)

[dieterdreist]

shows how the middle mouse button select menu is not visible entirely