Fix XML writeConcern parsing with numeric support

fixes code style issues to comply with doctrine/coding-standard:
- Adds space after `if` keyword
- Adds blank line after `if` block

Author: ikallali

lib/Doctrine/ODM/MongoDB/Mapping/Driver/XmlDriver.php

@@ -159,9 +159,10 @@ public function loadMetadataForClass($className, \Doctrine\Persistence\Mapping\C
 
         if (isset($xmlRoot['write-concern'])) {
             $writeConcern = (string) $xmlRoot['write-concern'];
-            if(is_numeric($writeConcern)) {
+            if (is_numeric($writeConcern)) {
                 $writeConcern = (int) $writeConcern;
             }
+            
             $metadata->setWriteConcern($writeConcern);
         }