Make -T _ and -B _ always set PL_laststatval

Make -T _ and -B _ always set PL_laststatval

-T _ and -B _ always do another stat() on the previous file handle or
filename, unless it is a handle that has been closed.

Normally, the internal stat buffer, status, etc., are reset even for
_.  This happens even on a failed fstat().

-T HANDLE and -B HANDLE currently *do* reset the stat status
(PL_laststatval) if there is no IO thingy, so having -T _ and -B _ not
do that makes things needlessly inconsistent.