pkt-line: check write_in_full() errors against "< 0"

As with the previous two commits, we prefer to check
write_in_full()'s return value to see if it is negative,
rather than comparing it to the input length.

These cases actually flip the logic to check for success,
making conversion a little different than in other cases. We
could of course write:

  if (write_in_full(...) >= 0)
          return 0;
  return error(...);

But our usual method of spelling write() error checks is
just "< 0". So let's flip the logic for each of these
conditionals to our usual style.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pkt-line.c

@@ -94,9 +94,9 @@ void packet_flush(int fd)
 int packet_flush_gently(int fd)
 {
 	packet_trace("0000", 4, 1);
-	if (write_in_full(fd, "0000", 4) == 4)
-		return 0;
-	return error("flush packet write failed");
+	if (write_in_full(fd, "0000", 4) < 0)
+		return error("flush packet write failed");
+	return 0;
 }
 
 void packet_buf_flush(struct strbuf *buf)
@@ -137,18 +137,17 @@ static int packet_write_fmt_1(int fd, int gently,
 			      const char *fmt, va_list args)
 {
 	struct strbuf buf = STRBUF_INIT;
-	ssize_t count;
 
 	format_packet(&buf, fmt, args);
-	count = write_in_full(fd, buf.buf, buf.len);
-	if (count == buf.len)
-		return 0;
-
-	if (!gently) {
-		check_pipe(errno);
-		die_errno("packet write with format failed");
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		if (!gently) {
+			check_pipe(errno);
+			die_errno("packet write with format failed");
+		}
+		return error("packet write with format failed");
 	}
-	return error("packet write with format failed");
+
+	return 0;
 }
 
 void packet_write_fmt(int fd, const char *fmt, ...)
@@ -183,9 +182,9 @@ static int packet_write_gently(const int fd_out, const char *buf, size_t size)
 	packet_size = size + 4;
 	set_packet_header(packet_write_buffer, packet_size);
 	memcpy(packet_write_buffer + 4, buf, size);
-	if (write_in_full(fd_out, packet_write_buffer, packet_size) == packet_size)
-		return 0;
-	return error("packet write failed");
+	if (write_in_full(fd_out, packet_write_buffer, packet_size) < 0)
+		return error("packet write failed");
+	return 0;
 }
 
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...)