Added if statements to TBTKExit and TBTKAssert, checking whether log is open or not before attempting to close it.
Added if statements to TBTKExit and TBTKAssert, checking whether log is open or not before attempting to close it.

dafer45/TBTK,dafer45/TBTK,dafer45/TBTK,dafer45/TBTK