Corrected basic checks: check for empty document, as well as empty areaTree...

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@672564 13f79535-47bb-0310-9956-ffa450edef68

test/layoutengine/basic-checks.xml

@@ -20,5 +20,6 @@
   This file contains basic checks that are performed for every tescase
 -->
 <checks>
-  <true xpath="/*" />
+  <true xpath="boolean(/areaTree)" />
+  <true xpath="boolean(/areaTree/*)" />
 </checks>