avoid a problem in catalog cleanup on SMP if catalogs were not

* catalog.c: avoid a problem in catalog cleanup on SMP if
  catalogs were not initialized.
Daniel
diff --git a/catalog.c b/catalog.c
index fca4022..a66b6f0 100644
--- a/catalog.c
+++ b/catalog.c
@@ -2869,6 +2869,9 @@
  */
 void
 xmlCatalogCleanup(void) {
+    if (xmlCatalogInitialized == 0)
+        return;
+
     xmlRMutexLock(xmlCatalogMutex);
     if (xmlDebugCatalogs)
 	xmlGenericError(xmlGenericErrorContext,