[mobs] Number value used as an entity reference

[Lymkwi]

The following crash occured multiple times this morning :

2015-11-28 12:12:50: ACTION[Server]: Gael-de-Sailly right-clicks object 10: LuaEntitySAO at (541,18.5,-1231)
2015-11-28 12:12:53: ERROR[Main]: UNRECOVERABLE error occurred. Stopping server. Please fix the following error:
2015-11-28 12:12:53: ERROR[Main]: Lua: Runtime error from mod 'boats' in callback luaentity_Step(): /home/quentinbd/mff/bin/../mods/mobs/api.lua:55: attempt to index local 'self' (a number value)
2015-11-28 12:12:53: ERROR[Main]: stack traceback:
2015-11-28 12:12:53: ERROR[Main]:   /home/quentinbd/mff/bin/../mods/mobs/api.lua:55: in function 'get_velocity'
2015-11-28 12:12:53: ERROR[Main]:   ...bin/../games/minetestforfun_game/mods/boats/init.lua:171: in function <...bin/../games/minetestforfun_game/mods/boats/init.lua:105>

In thread 7f82874d0740:
/home/quentinbd/mff/src/server.cpp:505: void Server::step(float): A fatal error occurred: Lua: Runtime error from mod 'boats' in callback luaentity_Step(): /home/quentinbd/mff/bin/../mods/mobs/api.lua:55: attempt to index local 'self' (a number value)
stack traceback:
    /home/quentinbd/mff/bin/../mods/mobs/api.lua:55: in function 'get_velocity'
    ...bin/../games/minetestforfun_game/mods/boats/init.lua:171: in function <...bin/../games/minetestforfun_game/mods/boats/init.lua:105>

[ghost]

Fixed 5e5bc34