Before 1c4e5cadf2 (Autosuggestions in multi-line command lines,
2024-12-15), the completion code path in the autosuggestion performer
used to do something weird: it used to request completions for the
entire command line (with the implied cursor at end) but try to apply
the same completion at the actual cursor.
That commit changed this to request completions only up to the cursor
position, which could in theory make us produce valid completions even
if the cursor is not at end of the line. However, that doesn't really
work since autosuggestions can only be rendered at the end of the line.
And the worst of it, that commit tries to compute
line_at_cursor(&full_line, search_string_range.end)
which crashes as out-of-bounds if the completion needs to replace the token
(like a case-correcting completion does).
Let's apply completions to the end, matching how autosuggestions work
in general.
d823444c6e