Check for false instead of null in ModuleEventRegistration

[fritzmg]

CalendarLeadsModel::findByLeadEventMail will return false here

calendar-extended-bundle/src/Resources/contao/models/CalendarLeadsModel.php

Lines 110 to 113 in 7364133

	$objResult = \Database::getInstance()->prepare($sql)->execute((int)$lid, "eventid", (int)$eid, "email", $mail);
	if (!$objResult || $objResult->numRows === 0) {
	return false;
	}

thus ModuleEventRegistration needs to check for false instead of null (see here.

Fixes #29

[kmielke]

Danke