Save query only when actually updating the schedule and not on OK

[arikfr]

Currently when you open the query schedule dialog and click on OK, it will save the query - even if no changes were made. This updates the query's updated_at timestamp and makes it hard to track when it was really changed.

Expected behavior: if no changes to the schedule were made, don't save the query even if OK was pressed.

[ranbena]

Actually, the schedule dialog is already set to save only if changed:

redash/client/app/components/queries/ScheduleDialog.jsx

Lines 181 to 189 in cfafa97

	// save if changed
	if (!isEqual(newSchedule, this.props.schedule)) {
	if (newSchedule.interval) {
	this.props.dialog.close(clone(newSchedule));
	} else {
	this.props.dialog.close(null);
	}
	}
	this.props.dialog.dismiss();

But I think it wasn't adapted to schedule = null after #3341.