Fixed #440.

[redboltz]

Fixed a pointer operation problem at msgpack::zone::chunk_list::clear().
It was only happened on C++03.

[leesatoh]

Hello. I will write here next message.

[leesatoh]

Hello.
I compiled the program with c++11 option. I think the Problem has been cleared..

[redboltz]

Thank you for testing. The expected behavior is follows:

Compiler	Before applying #440	After #440 applied
C++03	memory error	work well
C++11	work well	work well

Your program work well with C++03 after applied #440?

[leesatoh]

I download "After #440 applied".
I compiled the program in old environment(c++03), and execute.
It work well. I think this problem has been cleared.

[redboltz]

@leesatoh, thank you. I merge the PR.