Show text of selected non-truthy items

[hborchardt]

Hi, thanks a lot for this project!

When adding a SelectOption Interface with an item whose value is non-truthy (for example 0), this option's text should be shown when it is selected.

An example that I would like to use is this:

    node.addInputInterface('Input', 'SelectOption', undefined, {
        items: [{ text: "on", value: 1}, { text: "off", value: 0 }]
    });

Currently, when selecting "off", the this.value is 0, which is not truthy, so "" is shown as the selected value instead of "off".

With my change, we always try to get the corresponding text from the items list. If value is set to an option that is not in
the list of options, getItemByValue will return undefined, which will be converted to an empty string, as it was before.

[newcat]

Beautiful, thank you!