should not error for all_day events without date

fixes CORE-622
fixes CANVAS-3EPA

test plan
 - specs should pass

Change-Id: Ib824d38d51d35c8e97052019db6bcde2d5d37f8e
Reviewed-on: https://gerrit.instructure.com/132186
Tested-by: Jenkins
Reviewed-by: Felix Milea-Ciobanu <fmileaciobanu@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>

app/models/calendar_event.rb

@@ -666,7 +666,7 @@ class CalendarEvent < ActiveRecord::Base
         event.end.icalendar_tzid = 'UTC'
       end
 
-      if @event.all_day
+      if @event.all_day && @event.all_day_date
         event.start = Date.new(@event.all_day_date.year, @event.all_day_date.month, @event.all_day_date.day)
         event.start.ical_params = {"VALUE"=>["DATE"]}
         event.end = event.start

spec/models/calendar_event_spec.rb

@@ -184,6 +184,11 @@ describe CalendarEvent do
         expect(res.dtstamp.strftime('%Y-%m-%dT%H:%M:%S')).to eq Time.zone.parse("Sep 3 2008 12:05pm").in_time_zone('UTC').strftime('%Y-%m-%dT%H:%M:00')
       end
 
+      it 'should not fail with no date for all_day event' do
+        res = calendar_event_model(all_day: true).to_ics
+        expect(res).not_to be_nil
+      end
+
       it "should return string dates for all_day events" do
         calendar_event_model(:start_at => "Sep 3 2008 12:00am")
         expect(@event.all_day).to eql(true)