Fix "use after a free" (to be honnest that's more a segfault here) (CID 243)

modules/misc/xml/libxml.c

@@ -143,14 +143,14 @@ static xml_reader_t *ReaderCreate( xml_t *p_xml, stream_t *p_stream )
     p_reader = malloc( sizeof(xml_reader_t) );
     if( !p_reader )
     {
-        xmlFreeTextReader( p_reader->p_sys->p_reader );
+        xmlFreeTextReader( p_libxml_reader );
         return NULL;
     }
     p_reader->p_sys = p_sys = malloc( sizeof(xml_reader_sys_t) );
     if( !p_sys )
     {
+        xmlFreeTextReader( p_libxml_reader );
         free( p_reader );
-        xmlFreeTextReader( p_reader->p_sys->p_reader );
         return NULL;
     }
     p_reader->p_sys->p_reader = p_libxml_reader;