diff: remove dead code

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 b8d9c1a6
(2009-09-03,  diff.c: the builtin_diff() deals with only two-file
comparison).
Signed-off-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff.c

@@ -1252,14 +1252,6 @@ static void fn_out_consume(void *priv, char *line, unsigned long len)
 		return;
 	}
 
-	if (len < 1) {
-		emit_line(o, reset, reset, line, len);
-		if (ecbdata->diff_words
-		    && ecbdata->diff_words->type == DIFF_WORDS_PORCELAIN)
-			fputs("~\n", o->file);
-		return;
-	}
-
 	if (ecbdata->diff_words) {
 		if (line[0] == '-') {
 			diff_words_append(line, len,