Get more reliable elements when searching for the threadmark lists.

Do better verification.
Rework the logic so that it can handle the new threadmark formatting on SV
(as of May 21, 2017), which now has an extra ol list for the tabs at the top
of the threadmark page (for different threadmark types).

NetTally.Core/Input/Forums/Adapters/XenForoAdapter.cs

@@ -453,25 +453,31 @@ static IEnumerable<HtmlNode> GetThreadmarksList(IQuest quest, HtmlDocument page)
             {
                 var content = GetPageContent(page, PageType.Threadmarks);
 
-                var section = content.GetDescendantWithClass("div", "section");
+                var threadmarksDiv = content.GetDescendantWithClass("div", "threadmarks");
 
-                // Check a few different locations for the HTML list.
-                var list = section.Element("ol") ?? section.Descendants("ul").FirstOrDefault() ?? section.Descendants("ol").FirstOrDefault();
+                HtmlNode mainList = threadmarksDiv.Elements("ol").FirstOrDefault(e => e.HasClass("threadmarkList"));
 
-                if (list != null)
+                if (mainList == null)
                 {
-                    Predicate<HtmlNode> filterLambda = (n) =>
-                        (quest.UseCustomThreadmarkFilters && quest.ThreadmarkFilter.Match(n.InnerText)) ||
-                        (!quest.UseCustomThreadmarkFilters && DefaultThreadmarkFilter.Match(n.InnerText));
+                    mainList = threadmarksDiv.Elements("ul").FirstOrDefault(e => e.Elements("li").FirstOrDefault(a => a.HasClass("threadmarkItem")) != null);
+                }
 
-                    Func<HtmlNode, HtmlNode> nodeSelector = (n) => n.Element("a");
+                // Return empty list if no threadmark ul or ol found.
+                if (mainList == null)
+                    return new List<HtmlNode>();
 
-                    Func<HtmlNode, IEnumerable<HtmlNode>> childSelector = (i) => i.Element("ul")?.Elements("li") ?? i.Element("ol")?.Elements("li") ?? new List<HtmlNode>();
 
-                    var results = list.Elements("li").TraverseList(childSelector, nodeSelector, filterLambda);
+                Predicate<HtmlNode> filterLambda = (n) =>
+                    (quest.UseCustomThreadmarkFilters && quest.ThreadmarkFilter.Match(n.InnerText)) ||
+                    (!quest.UseCustomThreadmarkFilters && DefaultThreadmarkFilter.Match(n.InnerText));
 
-                    return results;
-                }
+                Func<HtmlNode, HtmlNode> nodeSelector = (n) => n.Element("a");
+
+                Func<HtmlNode, IEnumerable<HtmlNode>> childSelector = (i) => i.Element("ul")?.Elements("li") ?? new List<HtmlNode>();
+
+                var results = mainList.Elements("li").TraverseList(childSelector, nodeSelector, filterLambda);
+
+                return results;
             }
             catch (ArgumentNullException e)
             {