fix crash on rrule.between returned bad dates #3256 (#3257)

Fixes: #3256 

BUT.. the testcase is inconclusive.. as the code FAILS without the fix,
BUT somehow RETURNS 0 entries..
in real life run the node helper fails, and all calendar processing
stops.

tests/unit/modules/default/calendar/calendar_fetcher_utils_bad_rrule.js

@@ -0,0 +1,29 @@
+global.moment = require("moment-timezone");
+
+const CalendarFetcherUtils = require("../../../../../modules/default/calendar/calendarfetcherutils");
+
+describe("Calendar fetcher utils test", () => {
+	const defaultConfig = {
+		excludedEvents: []
+	};
+
+	describe("filterEvents", () => {
+		it("no events, not crash", () => {
+			const minusOneHour = moment().subtract(1, "hours").toDate();
+			const minusTwoHours = moment().subtract(2, "hours").toDate();
+			const plusOneHour = moment().add(1, "hours").toDate();
+			const plusTwoHours = moment().add(2, "hours").toDate();
+
+			const filteredEvents = CalendarFetcherUtils.filterEvents(
+				{
+					pastEvent: { type: "VEVENT", start: minusTwoHours, end: minusOneHour, summary: "pastEvent" },
+					ongoingEvent: { type: "VEVENT", start: minusOneHour, end: plusOneHour, summary: "ongoingEvent" },
+					upcomingEvent: { type: "VEVENT", start: plusOneHour, end: plusTwoHours, summary: "upcomingEvent" }
+				},
+				defaultConfig
+			);
+
+			expect(filteredEvents.length).toEqual(0);
+		});
+	});
+});