When `len < 1`, len has to be 0 or negative, emit_line will then remove the
first character and by then `len` would be negative. As this doesn't
happen, it is safe to assume it is dead code.
This continues to simplify the code, which was started in
b8d9c1a66b
(2009-09-03, diff.c: the builtin_diff() deals with only two-file
comparison).
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>