apply.c: split check_whitespace() into two

apply.c: split check_whitespace() into two

This splits the logic to record the presence of whitespace errors out of
the check_whitespace() function, which checks and then records.  The new
function, record_ws_error(), can be used by the blank-at-eof check that
does not use ws_check() logic to report its findings in the same output
format.

Signed-off-by: Junio C Hamano <redacted>