Prevent fatal on empty $mxfileXML #2

[4.2.x]

ERM32059

Change-Id: I00b795a8fe0367878d9117794a46aeaf741732e0

Author: it-spiderman

src/MXDocumentExtractor/Base.php

@@ -101,6 +101,9 @@ protected function getDiagramDOM( $mxfileXMLDOM ) {
 		$inflatedDiagramXML = base64_decode( $b64DiagramXML );
 		$urlencodedDiagramXML = gzinflate( $inflatedDiagramXML );
 		$diagramXmlString = urldecode( $urlencodedDiagramXML );
+		if ( empty( $diagramXmlString ) ) {
+			return null;
+		}
 		$documentXML = new DOMDocument();
 		$documentXML->loadXML( $diagramXmlString );