record_unwind_save_match_data in autocmp_chars

[Eli Zaretskii]

composite.c:autocmp_chars calls record_unwind_save_match_data before
it starts looping on an element of composition-function-table.
However, since the loop calls fast_looking_at, which is documented not
to change match data, is the call to record_unwind_save_match_data
really necessary?  If it is still necessary, what other functions
called by autocmp_chars might clobber match data?