Fix bug in parsing vCard data using PHP 7.3 due to an invalid regexp (#6744)

Looks like \R is not allowed in character class, but \r\n is fine.
On PHP 7.3.5 it throws warnings and empty result from preg_replace(),
though I couldn't reproduce.

CHANGELOG

@@ -3,6 +3,7 @@ CHANGELOG Roundcube Webmail
 
 - Managesieve: Fix so "Create filter" option does not show up when Filters menu is disabled (#6723)
 - Fix bug where bmp images couldn't be displayed on some systems (#6728)
+- Fix bug in parsing vCard data using PHP 7.3 due to an invalid regexp (#6744)
 
 RELEASE 1.3.9
 -------------

program/lib/Roundcube/rcube_vcard.php

@@ -536,7 +536,7 @@ class rcube_vcard
                 '/^item\d*\.X-AB.*$/mi',  // remove cruft like item1.X-AB*
                 '/^item\d*\./mi',         // remove item1.ADR instead of ADR
                 '/\n+/',                  // remove empty lines
-                '/^(N:[^;\R]*)$/m',      // if N doesn't have any semicolons, add some
+                '/^(N:[^;\r\n]*)$/m',     // if N doesn't have any semicolons, add some
             ),
             array(
                 '\2;type=\5\3:\4',