Ensure $select.selected exists prior to testing length.

[sime]

I have a use case where following exception is being thrown. To be honest I do not totally understand the execution path, but handling this exception seems obvious enough.

TypeError: Cannot read property 'length' of undefined at uis.directive.controller.ctrl.getPlaceholder

[user378230]

Appears to be in place already

ui-select/src/uiSelectMultipleDirective.js

Line 62 in 331f819

if($select.selected && $select.selected.length) return;

We should probably use isEmpty really though when I come to think about it.