Call the default constructors for value types so all fields are initialized.

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -1073,6 +1073,9 @@ namespace CppSharp.Generators.CSharp
                 PopIndent();
             }
 
+            if (@class.IsValueType)
+                WriteLineIndent(": this()");
+
             return hasBase;
         }