fix bsTypeahead: selected object display

bsTypeahead model $render handler tries to display the parsed selected item that the model value refers to but fails back to the model value itself when it can't find a match. It may happen if the model reference an object and if the source of candidate is always a an array with new items generated after each key strokes or select.

When it fails back to the model value itself. $render doesn't parse it for the display value.

The fix uses $parseOptions.displayValue on the modelValue in that case.

Fix for #1260