Typeahead allows me to clear the field when clearable is false

[carlhussey]

Please fill below information if issuing a bug report.

Expected behaviour

When I have clearable=false, I should not be able to clear out the value that is in the field. If I decide to begin searching and then remove the data by backspacing, I would expect the original value to still show up.

Actual behaviour

When I begin typing a result and then backspace and remove my search term, it lets me clear the field entirely and doesn't set the original value back.

Example: https://giphy.com/gifs/l0IsIbLEnkrpxBv8c/fullscreen

More Info

ng-select version: 0.2.5

browser: chrome

reproducable in demo page: yes if clearable=false