create index should avoid coredump

[vagetablechicken]

If we use sql_client, run create index i1 on t1(c1); with no options, ASTCreateIndexStatement::options_list() will be nullptr. It will core in

OpenMLDB/hybridse/src/planv2/ast_node_converter.cc

Line 1701 in d1edb4a

for (const auto option : root->options_list()->options_entries()) {

It's better to return error if no options? Or we can accept create index without ts settings?
P.S. we can set index without ts settings in create table .