Invalid regular expression error

[sigismund]

Few days ago I got error report triggered by user using Chrome (50.0).

Invalid regular expression: /^+/: Nothing to repeat

The culprit code can be found here:

.on('oninput' in $input[0] ? 'input' : 'keyup', function() {
  if ( $input.val().length ) {
    // Search in select options
    $.each(_this.items, function(i, elm) {
      if ( RegExp('^' + $input.val(), 'i').test(elm.slug) && !elm.disabled ) {
        _select(i);
        return false;
      }
    });
  }
});

Probably there should be an additional check if value is empty?