Fix for item.originalStartTime being undefined

[flying-sheep]

I sometimes get this otherwise:

TypeError: Cannot read property 'dateTime' of undefined
    at [unknown function](Helpers:493:44)
    at processEventInstance(Helpers:492:45)
    at startSync(Code:139:7)

in

GAS-ICS-Sync/Helpers.gs

Lines 492 to 497 in 763f219

	var eventInstanceToPatch = calendarEvents.filter(function(item){
	var origStart = item.originalStartTime.dateTime || item.originalStartTime.date;
	var instanceStart = new ICAL.Time.fromString(origStart);
	return (instanceStart.compare(recIDStart) == 0);
	});

[davideworsham]

I had the same error and this resolved it.

[derekantrican]

@flying-sheep Thank you for the PR. Did you happen to try @jonas0b1011001 's "DEV" version linked here?

(@davideworsham - same question)

Some people are responding saying they had success with that so I'll have to figure out which solution we want (or both)

[derekantrican]

@flying-sheep I haven't heard back from you and I think #151 will solve this so I'm going to close this PR