XML: throw an error if HTML subtitles have no root node

This shouldn't happen unless the codec is buggy

modules/misc/freetype.c

@@ -2181,11 +2181,20 @@ static int RenderHtml( filter_t *p_filter, subpicture_region_t *p_region_out,
                 /* Only text and karaoke tags are supported */
                 msg_Dbg( p_filter, "Unsupported top-level tag <%s> ignored.",
                          node );
-                p_filter->p_sys->p_xml = xml_ReaderReset( p_xml_reader, NULL );
-                p_xml_reader = NULL;
                 rv = VLC_EGENERIC;
             }
         }
+        else
+        {
+            msg_Err( p_filter, "Malformed HTML subtitle" );
+            rv = VLC_EGENERIC;
+        }
+
+        if( rv != VLC_SUCCESS )
+        {
+            p_filter->p_sys->p_xml = xml_ReaderReset( p_xml_reader, NULL );
+            p_xml_reader = NULL;
+        }
     }
 
     if( p_xml_reader )

modules/misc/quartztext.c

@@ -833,11 +833,22 @@ static int RenderHtml( filter_t *p_filter, subpicture_region_t *p_region_out,
                     else
                     {
                         /* Only text and karaoke tags are supported */
-                        xml_ReaderDelete( p_xml_reader );
-                        p_xml_reader = NULL;
+                        msg_Dbg( p_filter, "Unsupported top-level tag "
+                                           "<%s> ignored.", name );
                         rv = VLC_EGENERIC;
                     }
                 }
+                else
+                {
+                    msg_Err( p_filter, "Malformed HTML subtitle" );
+                    rv = VLC_EGENERIC;
+                }
+
+                if( rv != VLC_SUCCESS )
+                {
+                    xml_ReaderDelete( p_xml_reader );
+                    p_xml_reader = NULL;
+                }
             }
 
             if( p_xml_reader )