fix field not being clear when item change from outside the component

[Hugome]

When onSelectedItemChanged is called after a reactivity change from outside the component and the new selectedItem is undefined/null, the text keep the same previous value, but change the actual value.

The labelFunction/safeLabelFunction check if the selectedItem is undefined/null and set the correct empty string in the text

[Blitzlord]

Hey, I noticed the same issue.
When trying to change/clear the input from the outside (like in this example) by using undefined , the input text remains.