add default case for missing field in generated code

Author: Lewis Mohr

src/MsgPack/Serialization/AbstractSerializers/SerializerBuilder`3.Object.cs

@@ -436,10 +436,16 @@ private IEnumerable<TConstruct> EmitObjectUnpackFromMapCore( TContext context, T
 								unpackedKey =>
 									this.EmitStoreVariableStatement( context, key, unpackedKey )
 							);
+
 						var assigns =
 							this.EmitStringSwitchStatement(
 								context,
 								key,
+								this.EmitInvokeVoidMethod(
+									context,
+									context.Unpacker,
+									typeof( Unpacker ).GetMethod( "Skip" )
+								),
 								entries.Where( e => e.Member != null ).ToDictionary(
 									entry => entry.Contract.Name,
 									entry =>