patch 9.0.0761: cannot use 'indentexpr' for Lisp indenting

Problem:    Cannot use 'indentexpr' for Lisp indenting.
Solution:   Add the 'lispoptions' option.
diff --git a/src/buffer.c b/src/buffer.c
index 5f8512a..0849b70 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2390,6 +2390,7 @@
     clear_string_option(&buf->b_p_ft);
     clear_string_option(&buf->b_p_cink);
     clear_string_option(&buf->b_p_cino);
+    clear_string_option(&buf->b_p_lop);
     clear_string_option(&buf->b_p_cinsd);
     clear_string_option(&buf->b_p_cinw);
     clear_string_option(&buf->b_p_cpt);