fix(datepicker): ensure initDate is on an object

- Check if `options` is an object to avoid error at `initDate` check

Closes #3625

Author: kreigiron

Diff for: src/datepicker/datepicker.js

@@ -549,7 +549,7 @@ function ($compile, $parse, $document, $position, dateFilter, dateParser, datepi
 
       if ( attrs.datepickerOptions ) {
         var options = scope.$parent.$eval(attrs.datepickerOptions);
-        if(options.initDate) {
+        if(options && options.initDate) {
           scope.initDate = options.initDate;
           datepickerEl.attr( 'init-date', 'initDate' );
           delete options.initDate;