Modify CONCAT() arguments, because + operator requires them to be of type varchar (#1488505)

With SQL Server 2012 we can use just CONCAT(), but we need to support older versions

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Fix SQL query for contacts listing on MS SQL Server (#1488505)
 - Update to TinyMCE 3.5.2
 - Fix window.resize handler on IE8 and Opera (#1488453)
 - Don't let error message popups cover the login form (#1488500)

program/include/rcube_mdb2.php

@@ -648,6 +648,11 @@ class rcube_mdb2
             case 'mssql':
             case 'sqlsrv':
                 $delim = ' + ';
+                // Modify arguments, because + operator requires them to be of type varchar (#1488505)
+                // with SQL Server 2012 we can use just CONCAT(), but we need to support older versions
+                foreach ($args as $idx => $arg) {
+                    $args[$idx] = "CAST($arg AS varchar)";
+                }
                 break;
             default:
                 $delim = ' || ';