hush: add more complex case to leak testcase, fix found breakage

hush: add more complex case to leak testcase, fix found breakage

function                                             old     new   delta
unset_local_var_len                                    -     167    +167
run_list                                            2350    2457    +107
set_vars_and_save_old                                  -      87     +87
free_pipe                                            207     227     +20
builtin_unset                                        220     229      +9
builtin_exit                                          49      47      -2
free_strings_and_unset                                53       -     -53
set_vars_all_and_save_old                             87       -     -87
unset_local_var                                      168       -    -168
------------------------------------------------------------------------------
(add/remove: 2/3 grow/shrink: 3/1 up/down: 390/-310)           Total: 80 bytes

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