ash: add test for issue with here document

This used to work but doesn't now:

foo () {
cat <<EOF && { echo "$1" ; }
$1
EOF
}

foo "bar"

Reported-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-heredoc/heredoc2.right

@@ -0,0 +1,2 @@
+bar
+bar

shell/ash_test/ash-heredoc/heredoc2.tests

@@ -0,0 +1,7 @@
+foo () {
+cat <<EOF && { echo "$1" ; }
+$1
+EOF
+}
+
+foo "bar"