assertion failed if you press "up/down" button in an empty message window

[Angelo Locritani]

Pressing up/down on an empty news list causes a crash because of failure of the following assertion:

src/ui_basic/table.h:199: void* UI::Table<void*>::operator[](uint32_t) const: assertion `i < m_entry_records.size()' failed.

this is an extract of backtrace (complete backtrace attached)
[...]
#20 0x084f842e in UI::Table<void*>::select (this=0x102ad998, i=0)
    at src/ui_basic/table.cc:446
#21 0x084f839b in UI::Table<void*>::move_selection (this=0x102ad998, offset=1)
    at src/ui_basic/table.cc:421
#22 0x084f8039 in UI::Table<void*>::handle_key (this=0x102ad998, down=true, code=...)
    at src/ui_basic/table.cc:337
#23 0x08720e61 in GameMessageMenu::handle_key (this=0x102a96c0, down=true, code=...)
    at src/wui/game_message_menu.cc:273
[...]

[SirVer (sirver)]

Released in build17-rc1.