ash: fix ifs cleanup on error paths

Patch by Alex Gorinson <algore3698@gmail.com>

function                                             old     new   delta
evalvar                                              477     495     +18
varvalue                                             603     618     +15
subevalvar                                          1557    1572     +15
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 48/0)               Total: 48 bytes

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