Prevent potential PHP8.2 warnings

Method setEmailAddresses now ensures that entry in tb_configuration
table contains either valid string, or does not exists. Therefore, null
value should never be stored in tb_configuration table for
COLLECTLOGS_NEW_ERRORS_EMAIL configuration key.

However, previous version of module did not do this check, so in some
cases NULL is actually stored inside db table.

Let's account for this situation.

Closes #8

classes/Settings.php

@@ -186,7 +186,7 @@ public function setSendNewErrorsEmail($value)
     public function getEmailAddresses()
     {
         $strValue = Configuration::getGlobalValue(static::SETTINGS_NEW_ERRORS_EMAIL_ADDRESSES);
-        if ($strValue === false) {
+        if (is_null($strValue) || $strValue === false) {
             return [];
         }
         return explode("\n", $strValue);