fix SELECT border for valid/invalid state
fix SELECT border for valid/invalid state

At the moment adding `valid`/`invalid` classes to the SELECT's input produces a greyish border.
Dogfalo/materialize,ccloli/materialize,ccloli/materialize,INGCRENGIFO/materialize,tomscholz/materialize,digitalkaoz/materialize,digitalkaoz/materialize,INGCRENGIFO/materialize,Dogfalo/materialize,tomscholz/materialize,ZiperRom1/materialize,ZiperRom1/materialize