hush: fix handling of } which is not a closing one in { cmd; }

function                                             old     new   delta
parse_stream                                        2176    2302    +126
builtin_unset                                        381     387      +6

diff --git a/shell/hush_test/hush-vars/var_posix1.right b/shell/hush_test/hush-vars/var_posix1.right
index 373b16c..47d52a6 100644
--- a/shell/hush_test/hush-vars/var_posix1.right
+++ b/shell/hush_test/hush-vars/var_posix1.right
@@ -22,6 +22,7 @@
 babcdcd
 ababcdcd
 Empty:
+ababcdcd}_tail
 ababcd
 ababcd
 ababcd
@@ -30,4 +31,5 @@
 ababcdc
 ababcdcd
 Empty:
+ababcdcd}_tail
 end