combase: When looking up an apartment which has a given creator thread ID use multi-threaded apartment only if the thread doesn't have an apartment-threaded one.

CoIncrementMTAUsage() always creates the MTA if it doesn't already exist,
and mta->tid may accidently match the apt->tid of the apartment-threaded
apartment of the thread.
Signed-off-by: Dmitry Timoshkov <dmitry@baikal.ru>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>