Introduce osl_areCommandArgsSet.

We cannot call osl_setCommandArgs twice, however there is currently
no way to determine whether or not this has already been done. This is
necessary e.g. for LibreOfficeKit where we may also be using UNO
separately (and also for unit tests where LO is already set-up prior
to the unit test running, and therefore we can't set up osl again
from within LOK).

Change-Id: Id1f357ef604eb2b6b7814c9a04ac6933a39fd3eb