hush: fix handling of empty heredoc EOF marker

function                                             old     new   delta
parse_stream                                        2609    2634     +25

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-heredoc/heredoc_empty2.right b/shell/ash_test/ash-heredoc/heredoc_empty2.right
new file mode 100644
index 0000000..e32c6ea
--- /dev/null
+++ b/shell/ash_test/ash-heredoc/heredoc_empty2.right
@@ -0,0 +1,4 @@
+OK1
+Ok:0
+OK2
+Ok:0
diff --git a/shell/ash_test/ash-heredoc/heredoc_empty2.tests b/shell/ash_test/ash-heredoc/heredoc_empty2.tests
new file mode 100755
index 0000000..20fc35f
--- /dev/null
+++ b/shell/ash_test/ash-heredoc/heredoc_empty2.tests
@@ -0,0 +1,14 @@
+unset a
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK1
+
+echo Ok:$?
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK2
+	
+
+echo Ok:$?