don't leak the internal documents, but properly delete them

svn path=/trunk/KDE/kdegraphics/okular/; revision=719297

generators/xps/generator_xps.cpp

@@ -1302,6 +1302,7 @@ bool XpsFile::closeDocument()
 
     m_docInfo = 0;
 
+    qDeleteAll( m_documents );
     m_documents.clear();
 
     delete m_xpsArchive;