removed a memory leak remaining from the switch to a dictionnary for

* xmlschemas.c: removed a memory leak remaining from the switch
  to a dictionnary for string allocations c.f. #130891
Daniel
diff --git a/xmlschemas.c b/xmlschemas.c
index 539465f..d639b67 100644
--- a/xmlschemas.c
+++ b/xmlschemas.c
@@ -4897,7 +4897,7 @@
             return (NULL);
         }
         doc->URL = xmlStrdup(BAD_CAST "in_memory_buffer");
-        ctxt->URL = xmlStrdup(BAD_CAST "in_memory_buffer");
+        ctxt->URL = xmlDictLookup(ctxt->dict, BAD_CAST "in_memory_buffer", -1);
     } else if (ctxt->doc != NULL) {
         doc = ctxt->doc;
     } else {