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

shell/hush_test/hush-parsing/group1.right

@@ -0,0 +1 @@
+word} }

shell/hush_test/hush-parsing/group1.tests

@@ -0,0 +1 @@
+{ echo word} }; }