hush: make "wait %1" work even if the job is dead

hush: make "wait %1" work even if the job is dead

Example script:

	sleep 1 | (sleep 1;exit 3) &
	sleep 2
	echo Zero:$?
	wait %1
	echo Three:$?

function                                             old     new   delta
clean_up_last_dead_job                                 -      24     +24
process_wait_result                                  426     447     +21
builtin_wait                                         285     293      +8
insert_job_into_table                                264     269      +5
builtin_jobs                                          68      73      +5
remove_job_from_table                                 59      57      -2
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/1 up/down: 63/-2)              Total: 61 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>