Restore behavior of htmlDocContentDumpFormatOutput()

Patch by J Pascoe of Apple.

* HTMLtree.c:
(htmlDocContentDumpFormatOutput):
- Prior to commit b79ab6e6d9, xmlDoc.type was set to
  XML_HTML_DOCUMENT_NODE before dumping the HTML output, then
  restored before returning.

HTMLtree.c

@@ -987,7 +987,14 @@ void
 htmlDocContentDumpFormatOutput(xmlOutputBufferPtr buf, xmlDocPtr cur,
 	                       const char *encoding ATTRIBUTE_UNUSED,
                                int format) {
+    int type = 0;
+    if (cur) {
+        type = cur->type;
+        cur->type = XML_HTML_DOCUMENT_NODE;
+    }
     htmlNodeDumpFormatOutput(buf, cur, (xmlNodePtr) cur, NULL, format);
+    if (cur)
+        cur->type = (xmlElementType) type;
 }
 
 /**