This cleanup small code and let catch some missing check cases
when 0 guid attempt searched by real DB query.
This also make function call more safe if it used with non-player guid by
some reason.
Now safe allow this casts in like way after completed convertion to ObjectGuid use.
Also simplify code in result allowed auto cast to uint64.
Please _not_ add new uint64 storages (local and in structures) for guid values.