hush: fix heredoc handling in the "cmd <<EOF ;<newline>" case

function                                             old     new   delta
parse_stream                                        2759    2787     +28

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

shell/ash_test/ash-heredoc/heredocA.right

@@ -0,0 +1 @@
+Ok

shell/ash_test/ash-heredoc/heredocA.tests

@@ -0,0 +1,4 @@
+{ cat <<EOF ;
+Ok
+EOF
+}