Fix NullReferenceException in invalid XAML files that have a property as root element.

src/AddIns/BackendBindings/XamlBinding/XamlBinding/CompilationUnitCreatorVisitor.cs

@@ -151,7 +151,9 @@ namespace ICSharpCode.XamlBinding
 				c.Modifiers |= ModifierEnum.Public;
 			
 			c.Region = CreateRegion(element.StartOffset, element.EndOffset);
-			c.BaseTypes.Add(TypeFromXmlNode(CompilationUnit, element));
+			var baseType = TypeFromXmlNode(CompilationUnit, element);
+			if (baseType != null)
+				c.BaseTypes.Add(baseType);
 			CompilationUnit.Classes.Add(c);
 
 			DefaultMethod initializeComponent = new DefaultMethod(

src/AddIns/BackendBindings/XamlBinding/XamlBinding/CompletionDataHelper.cs

@@ -264,7 +264,7 @@ namespace ICSharpCode.XamlBinding
 				
 				string key = string.IsNullOrEmpty(lastElement.Prefix) ? "" : lastElement.Prefix + ":";
 				
-				if (context.ParentElement.LocalName.StartsWith(lastElement.LocalName.TrimEnd('.'), StringComparison.OrdinalIgnoreCase)) {
+				if (context.ParentElement != null && context.ParentElement.LocalName.StartsWith(lastElement.LocalName.TrimEnd('.'), StringComparison.OrdinalIgnoreCase)) {
 					AddAttributes(rt, list, includeEvents);
 					AddAttachedProperties(rt.GetUnderlyingClass(), list, key, lastElement.Name.Trim('.'));
 				} else