Improve XML serialization, URI parsing, and XPath node set processing.

third_party/libxml/src/valid.c

Index: third_party/libxml/src/valid.c
diff --git a/third_party/libxml/src/valid.c b/third_party/libxml/src/valid.c
index 19f84b826233895d0bd91e6bac6fcd6bf714546c..26d72210f9a6fa1992c8fc87dc934f973570abd9 100644
--- a/third_party/libxml/src/valid.c
+++ b/third_party/libxml/src/valid.c
@@ -1172,12 +1172,14 @@ xmlDumpElementContent(xmlBufferPtr buf, xmlElementContentPtr content, int glob)
 	    xmlBufferWriteCHAR(buf, content->name);
 	    break;
 	case XML_ELEMENT_CONTENT_SEQ:
+	    if (content->c1 == NULL) return;
 	    if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
 	        (content->c1->type == XML_ELEMENT_CONTENT_SEQ))
 		xmlDumpElementContent(buf, content->c1, 1);
 	    else
 		xmlDumpElementContent(buf, content->c1, 0);
             xmlBufferWriteChar(buf, " , ");
+	    if (content->c2 == NULL) return;
 	    if ((content->c2->type == XML_ELEMENT_CONTENT_OR) ||
 	        ((content->c2->type == XML_ELEMENT_CONTENT_SEQ) &&
 		 (content->c2->ocur != XML_ELEMENT_CONTENT_ONCE)))
@@ -1186,12 +1188,14 @@ xmlDumpElementContent(xmlBufferPtr buf, xmlElementContentPtr content, int glob)
 		xmlDumpElementContent(buf, content->c2, 0);
 	    break;
 	case XML_ELEMENT_CONTENT_OR:
+	    if (content->c1 == NULL) return;
 	    if ((content->c1->type == XML_ELEMENT_CONTENT_OR) ||
 	        (content->c1->type == XML_ELEMENT_CONTENT_SEQ))
 		xmlDumpElementContent(buf, content->c1, 1);
 	    else
 		xmlDumpElementContent(buf, content->c1, 0);
             xmlBufferWriteChar(buf, " | ");
+	    if (content->c2 == NULL) return;
 	    if ((content->c2->type == XML_ELEMENT_CONTENT_SEQ) ||
 	        ((content->c2->type == XML_ELEMENT_CONTENT_OR) &&
 		 (content->c2->ocur != XML_ELEMENT_CONTENT_ONCE)))