[yelp] Check whether document has a root element before accessing it

[David King <davidk src gnome org>]

commit e7f03bfb6e28ebadc1bf5c5b615ad0f90e0e2bb3
Author: Tomas Popela <tpopela redhat com>
Date:   Mon Jul 23 09:50:53 2018 +0200

    Check whether document has a root element before accessing it
    
    yelp-3.28.1/libyelp/yelp-docbook-document.c:562:13: note: Access to field 'ns' results in a dereference 
of a null pointer (loaded from field 'xmlcur')
            if (priv->xmlcur->ns) {
                ^     ~~~~~~
      560|            * unique value, and insert it into the in-memory tree */
      561|           g_snprintf (autoidstr, 20, "//autoid-%d", ++autoid);
      562|->         if (priv->xmlcur->ns) {
      563|               xmlNewNsProp (priv->xmlcur,
      564|                             xmlNewNs (priv->xmlcur, XML_XML_NAMESPACE, BAD_CAST "xml"),
    
    yelp-3.28.1/libyelp/yelp-docbook-document.c:608:16: note: Access to field 'children' results in a 
dereference of a null pointer (loaded from field 'xmlcur')
        for (cur = priv->xmlcur->children; cur; cur = cur->next) {
                   ^     ~~~~~~
      606|                                 NULL);
      607|
      608|->     for (cur = priv->xmlcur->children; cur; cur = cur->next) {
      609|           if (cur->type == XML_ELEMENT_NODE) {
      610|               priv->xmlcur = cur;

 libyelp/yelp-docbook-document.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/libyelp/yelp-docbook-document.c b/libyelp/yelp-docbook-document.c
index 893732c0..9557427f 100644
--- a/libyelp/yelp-docbook-document.c
+++ b/libyelp/yelp-docbook-document.c
@@ -316,6 +316,7 @@ docbook_process (YelpDocbookDocument *docbook)
     GFile *file = NULL;
     gchar *filepath = NULL;
     xmlDocPtr xmldoc = NULL;
+    xmlNodePtr xmlcur = NULL;
     xmlChar *id = NULL;
     xmlParserCtxtPtr parserCtxt = NULL;
     GError *error;
@@ -350,7 +351,10 @@ docbook_process (YelpDocbookDocument *docbook)
                               XML_PARSE_DTDLOAD | XML_PARSE_NOCDATA |
                               XML_PARSE_NOENT   | XML_PARSE_NONET   );
 
-    if (xmldoc == NULL) {
+    if (xmldoc)
+        xmlcur = xmlDocGetRootElement (xmldoc);
+
+    if (xmldoc == NULL || xmlcur == NULL) {
         error = g_error_new (YELP_ERROR, YELP_ERROR_PROCESSING,
                              _("The file ‘%s’ could not be parsed because it is"
                                " not a well-formed XML document."),
@@ -381,7 +385,7 @@ docbook_process (YelpDocbookDocument *docbook)
         priv->max_depth = 1;
 
     priv->xmldoc = xmldoc;
-    priv->xmlcur = xmlDocGetRootElement (xmldoc);
+    priv->xmlcur = xmlcur;
 
     id = xmlGetProp (priv->xmlcur, BAD_CAST "id");
     if (!id)