fix(lua): str_byteindex() can return an index past the end #41766

Problem:
For an incomplete sequence at the end of the string, utf_ptr2len_len()
reports more bytes than are there, and mb_utf_index_to_bytes() returns
that position unclamped:

    vim.str_byteindex('ab\xf0\x9f', 'utf-16', 3, false)  --> 6

on a 4 byte string. LSP callers use the result as a column, so
nvim_buf_set_extmark() then fails with "Invalid 'col': out of range".

Solution:
Clamp the returned byte index to the length of the string.

AI-assisted

0 files changed, 0 insertions, 0 deletions