Fix dropdown position when use data-size attribute

[smiglu]

When select has a lot of option (in my case 100+) I wanted to limit it to display only the 6 options with scroll. I use attribute data-size set to 6. But when i click to open select, isDropup flag is set to true, and option show above a select but is enough space to display options below button.

Fix #2766

[NicolasCARPi]

I can't reproduce the issue you describe (with select appearing as dropup). Could you try and have a reproducible case in tests that shows that your fix is useful?