Whitespace sometimes causes infinite loop

[Shkoklev]

When the option cleanUserText is set to false and the search function returns at least one item in the dropdown, if we try to append a whitespace character to the search term, an infinite loop is triggered and the component freezes

The infinite loop is triggered in the highlightFilter function because the 'keywords' parameter contains an empty string as an element of the array.

[azmeuk]

Fixed by #160