Save default DownloadBehaviour on a DMSDocument when initially uploading a new one

- array key check for behavior before using

code/model/DMSDocument.php

@@ -1011,12 +1011,14 @@ class DMSDocument extends DataObject implements DMSDocumentInterface
             $possibleBehaviors = $this->dbObject('DownloadBehavior')
                 ->enumValues();
 
+            if (array_key_exists($defaultDownloadBehaviour, $possibleBehaviors)) {
                 $behavior = $possibleBehaviors[$defaultDownloadBehaviour];
                 if ($behavior) {
                     $this->DownloadBehavior = $behavior;
                 }
             }
         }
+    }
 
     /**
      * Return the relative URL of an icon for the file type, based on the