vim-patch:9.0.1492: using uninitialized memory when argument is missing (#23351)

Problem:    Using uninitialized memory when argument is missing.
Solution:   Check there are sufficient arguments before the base.
            (closes vim/vim#12302)

https://github.com/vim/vim/commit/b7f2270bab102d68f83a6300699b7f98efad81f2



Co-authored-by: Bram Moolenaar <Bram@vim.org>