use doctrine to construct concat expression

apps/files/appinfo/update.php

@@ -3,14 +3,7 @@
 // fix webdav properties,add namespace in front of the property, update for OC4.5
 $installedVersion=OCP\Config::getAppValue('files', 'installed_version');
 if (version_compare($installedVersion, '1.1.6', '<')) {
-	// SQL92 string concatenation is ||, some of the DBMS don't know that
-	if (OC_Config::getValue('dbtype') === 'mysql') {
-		$concat = "concat('{DAV:}', `propertyname`)";
-	} else if (OC_Config::getValue('dbtype') === 'mssql') {
-		$concat = "'{DAV:}' + `propertyname`";
-	} else {
-		$concat = "'{DAV:}' || `propertyname`";
-	}
+	$concat = OC_DB::getConnection()->getDatabasePlatform()->getConcatExpression( "'{DAV:}'", "`propertyname`" );
 	$query = OC_DB::prepare( "UPDATE  `*PREFIX*properties`
 								  SET `propertyname` = $concat
 								WHERE `propertyname` LIKE '{%'" );