belt & braces

occasionally paste without meta attribute are encountered (while they are written), leading to:

PHP Warning:  Trying to access array offset on false in /srv/bin/administration on line 287
PHP Fatal error:  Uncaught TypeError: array_key_exists(): Argument #2 ($array) must be of type array, null given in /srv/bin/administration:287
Stack trace:
#0 /srv/bin/administration(287): array_key_exists()
#1 /srv/bin/administration(398): PrivateBin\Administration->_statistics()
#2 /srv/bin/administration(403): PrivateBin\Administration->__construct()
#3 {main}
  thrown in /srv/bin/administration on line 287

bin/administration

@@ -284,6 +284,7 @@ EOT, PHP_EOL;
             ++$counters['progress'];
 
             if (
+                array_key_exists('meta', $paste) &&
                 array_key_exists('expire_date', $paste['meta']) &&
                 $paste['meta']['expire_date'] < $time
             ) {