lei: clean up pkt_op consumer on exception, too

lei: clean up pkt_op consumer on exception, too

We need to consistently ensure pkt_op_c doesn't lead to a
long-lived circular reference if an exception is thrown in
pre_augment.  Maybe the API could be better, but this fixes an
FD leak when attempting to --augment a FIFO.

Followup-to: b9524082ba39e665 ("lei_xsearch: cleanup {pkt_op_p} on exceptions")