fix(menufield): Fix TypeError when no item is selected
fix(menufield): Fix TypeError when no item is selected

Prevents "TypeError: Cannot read property 'text' of null" in MenuField from being thrown when the listView.currentItem is nothing.

- Closes #272

AnonymHax/qml-material,jgab-net/qml-material,nathanhourt/qml-material,hunt978/qml-material,oKcerG/qml-material,hunt978/qml-material,jgab-net/qml-material,johnsog/qml-material,osechet/qml-material,ricardomv/qml-material,jgab-net/qml-material,oKcerG/qml-material,jneidlinger/qml-material,benevo-qml/qml-material,benevo-qml/qml-material,AnonymHax/qml-material,ricardomv/qml-material,jneidlinger/qml-material,benevo-qml/qml-material,oKcerG/qml-material,papyros/qml-material,papyros/qml-material,osechet/qml-material,jgab-net/qml-material,johnsog/qml-material,jneidlinger/qml-material,hunt978/qml-material,nathanhourt/qml-material,nathanhourt/qml-material,benevo-qml/qml-material,AnonymHax/qml-material,ricardomv/qml-material,osechet/qml-material,hunt978/qml-material,osechet/qml-material,johnsog/qml-material,oKcerG/qml-material,AnonymHax/qml-material,ricardomv/qml-material,nathanhourt/qml-material,papyros/qml-material,jneidlinger/qml-material,papyros/qml-material,johnsog/qml-material