handle_labels(): Fix problem for document fragments containing more

	than one "root" that prevented all the <label id=...> items
	from being promoted to id attributes on the enclosing chapter/
	section/... properly.

Doc/tools/sgmlconv/docfixer.py

@@ -165,7 +165,9 @@ def handle_appendix(doc):
 
 
 def handle_labels(doc):
-    labels = doc.getElementsByTagName("label")
+    for node in doc.childNodes:
+        if node.nodeType == xml.dom.core.ELEMENT:
+            labels = node.getElementsByTagName("label")
             for label in labels:
                 id = label.getAttribute("id")
                 if not id: