[server] Fix out of index acceses

This is reported as warning on CentOS 6.5:

    HatoholArmPluginInterface.cc: In static member function 'static ItemDataPtr HatoholArmPluginInterface::createItemData(mlpl::SmartBuffer&)':
    HatoholArmPluginInterface.cc:592: warning: array subscript is above array bounds
Merge pull request #526 from project-hatohol/server-fix-out-of-index-access

[server] Fix out of index acceses