Fix PHP warnings on dummy QUOTA responses in Courier-IMAP 4.17.1 (#6374)

CHANGELOG

@@ -1,6 +1,8 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Fix PHP warnings on dummy QUOTA responses in Courier-IMAP 4.17.1 (#6374)
+
 RELEASE 1.3.7
 -------------
 - Fix PHP Warning: Use of undefined constant IDNA_DEFAULT on systems without php-intl (#6244)

program/lib/Roundcube/rcube_imap_generic.php

@@ -3126,6 +3126,11 @@ class rcube_imap_generic
                     list(, , $quota_root) = $this->tokenizeResponse($line, 3);
 
                     $quotas = $this->tokenizeResponse($line, 1);
+
+                    if (empty($quotas)) {
+                        continue;
+                    }
+
                     foreach (array_chunk($quotas, 3) as $quota) {
                         list($type, $used, $total) = $quota;
                         $type = strtolower($type);