hush: fix a bug where we were requiring semicolon here: (cmd;)

also fix a bug where after error prompt is not shown.

function                                             old     new   delta
parse_stream                                        1612    1638     +26
parse_and_run_stream                                 361     375     +14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 40/0)               Total: 40 bytes

shell/hush_test/hush-misc/colon.tests

@@ -1,6 +1,5 @@
 false
 :
 echo $?
-# Extra ; after done is due to a bug
-(while :; do exit; done;)
+(while :; do exit; done)
 echo OK: $?