Replace remaining occurrences of "0001-01-01" with DBA::NULL_DATE

mod/hovercard.php

@@ -107,7 +107,7 @@ function hovercard_content()
 		'about'    => $contact['about'],
 		'network'  => Strings::formatNetworkName($contact['network'], $contact['url']),
 		'tags'     => $contact['keywords'],
-		'bd'       => $contact['birthday'] <= '0001-01-01' ? '' : $contact['birthday'],
+		'bd'       => $contact['birthday'] <= DBA::NULL_DATE ? '' : $contact['birthday'],
 		'account_type' => Contact::getAccountType($contact),
 		'actions'  => $actions,
 	];

mod/profiles.php

@@ -216,7 +216,7 @@ function profiles_post(App $a) {
 		} else {
 			$ignore_year = false;
 		}
-		if (!in_array($dob, ['0000-00-00', '0001-01-01'])) {
+		if (!in_array($dob, ['0000-00-00', DBA::NULL_DATE])) {
 			if (strpos($dob, '0000-') === 0 || strpos($dob, '0001-') === 0) {
 				$ignore_year = true;
 				$dob = substr($dob, 5);