Fix PoeditListCtrl::Model::GetValueByRow
Fix PoeditListCtrl::Model::GetValueByRow

Commit b33970a replaced wxBitmap by wxIcon but
PoeditListCtrl::Model::GetValueByRow was still assuming that
wxBitmap were manipulated, leading to error messages
"Wrong type, required: wxBitmap but: wxIcon" at runtime.

Fixes #571.

PKRoma/poedit,alexhenrie/poedit,PKRoma/poedit,PKRoma/poedit,nawawi/poedit,vslavik/poedit,nawawi/poedit,alexhenrie/poedit,nawawi/poedit,alexhenrie/poedit,vslavik/poedit,alexhenrie/poedit,PKRoma/poedit,nawawi/poedit,vslavik/poedit,nawawi/poedit,vslavik/poedit,vslavik/poedit,alexhenrie/poedit,PKRoma/poedit