Fix FormatException in Class Diagram addin.

Visual Studio class diagrams do not store the Collapsed xml attribute when the item is not collapsed.

src/AddIns/DisplayBindings/ClassDiagram/ClassCanvas/ClassCanvas.csproj

@@ -78,6 +78,7 @@
     <Compile Include="Shapes\RouteInheritanceShape.cs" />
     <Compile Include="Shapes\RouteShape.cs" />
     <Compile Include="Shapes\PropertyShape.cs" />
+    <Compile Include="Src\XPathNavigatorExtensions.cs" />
     <EmbeddedResource Include="Src\ClassCanvas.resx">
       <DependentUpon>ClassCanvas.Designer.cs</DependentUpon>
     </EmbeddedResource>

src/AddIns/DisplayBindings/ClassDiagram/ClassCanvas/Src/ClassCanvasItem.cs

@@ -625,7 +625,7 @@ namespace ClassDiagram
 		{
 			base.LoadFromXml(navigator);
 			
-			Collapsed = bool.Parse(navigator.GetAttribute("Collapsed", ""));
+			Collapsed = navigator.GetBooleanAttribute("Collapsed");
 			
 			XPathNodeIterator compNI = navigator.Select("Compartments/Compartment");
 			while (compNI.MoveNext())
@@ -634,7 +634,7 @@ namespace ClassDiagram
 				InteractiveHeaderedItem grp;
 				if (groupsByName.TryGetValue(compNav.GetAttribute("Name", ""), out grp))
 				{
-					grp.Collapsed = bool.Parse(compNav.GetAttribute("Collapsed", ""));
+					grp.Collapsed = compNav.GetBooleanAttribute("Collapsed");
 				}
 			}
 		}

src/AddIns/DisplayBindings/ClassDiagram/ClassCanvas/Src/XPathNavigatorExtensions.cs

@@ -0,0 +1,21 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
+// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
+
+using System;
+using System.Xml.XPath;
+
+namespace ClassDiagram
+{
+	public static class XPathNavigatorExtensions
+	{
+		public static bool GetBooleanAttribute(this XPathNavigator navigator, string name, string namespaceUri = "")
+		{
+			string attributeValue = navigator.GetAttribute(name, namespaceUri);
+			bool result = false;
+			if (bool.TryParse(attributeValue, out result)) {
+				return true;
+			}
+			return false;
+		}
+	}
+}