fix(ui5-daypicker): date selection range light blue indication (#6836)

When selecting a date range in the Calendar with selection mode Range, if you select a new start date (and thus have only one date selected), a range of dates have their background color set to light blue indicating they are in the selected date range. This is incorrect since there is only one date selected and therefore no date range yet.

Fixes #6781

packages/main/src/DayPicker.ts

@@ -712,7 +712,7 @@ class DayPicker extends CalendarPart implements ICalendarPicker {
 	 * @private
 	 */
 	_updateSecondTimestamp() {
-		if (this.selectionMode === CalendarSelectionMode.Range && this.selectedDates.length === 1) {
+		if (this.selectionMode === CalendarSelectionMode.Range && (this.selectedDates.length === 1 || this.selectedDates.length === 2)) {
 			this._secondTimestamp = this.timestamp;
 		}
 	}