Adding vertical padding to MenuItemStyleData causes menuHeights wrong calculations and eventually menu disappears

[pawlowskim]

I wanted to implement list with dividers, so I used customHeights for MenuItemStyleData. If I add vertical padding along with customHeights it causes odd behaviour. Like, each time dropdown is opened height for each row is reduced by the vertical padding. Eventually menu is not visible at all, because customHeights (in _DropdownRoute constructor) are all zeros.

On the other hand, when setting hardcoded height it works.

Example code could be taken from 3. DropdownButton2 with items of different heights like dividers, just add the vertical padding to the MenuItemStyleData