Fix sequential statements are emitted strangely in .net standard 2.0 code DOM.

This commit solves this behavior with early evaluation of iterators which are sequential statement body.

Author: yfakariya

src/MsgPack/Serialization/CodeDomSerializers/CodeDomSerializerBuilder.cs

@@ -354,7 +354,7 @@ protected override CodeDomConstruct EmitSequentialStatements( CodeDomContext con
 			statements = statements.ToArray();
 			Contract.Assert( statements.All( c => c.IsStatement ) );
 #endif
-			return CodeDomConstruct.Statement( statements.SelectMany( s => s.AsStatements() ) );
+			return CodeDomConstruct.Statement( statements.SelectMany( s => s.AsStatements().ToArray() ) );
 		}
 
 		[System.Diagnostics.CodeAnalysis.SuppressMessage( "Microsoft.Design", "CA1062:ValidateArgumentsOfPublicMethods", MessageId = "0", Justification = "Validated internally" )]
@@ -1715,4 +1715,4 @@ protected override CodeDomContext CreateCodeGenerationContextForSerializerCreati
 #endif // DEBUG
 		}
 	}
-}
+}