Fix for GetCurrentLocation when stack is empty.
Fix for GetCurrentLocation when stack is empty.

GetCurrentLocation now returns a dummy value and line number when the
stack is empty. This prevents problems with logging during locking when
a thread tries to join, where its stack would be empty.

Change-Id: Ib49ac6fd86655bce579524bf7f165e95ae829d9a

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst