In osrf_system_shutdown(): provide a return value for an early

In osrf_system_shutdown(): provide a return value for an early
return (since the function is of type int).

It's not clear whether these are the right semantics, since we
never capture the return value anyway.  But if we're going
to return anything at all, it makes sense to return something
different in the case of an early return.

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1688 9efc2488-bf62-4759-914b-345cdb29e865