image/gif: avoid unused assignment

Change-Id: Iaaecd8be9268c923f40cf0e5153cbf79f7015b8d
Reviewed-on: https://go-review.googlesource.com/13892Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/image/gif/writer.go

@@ -83,7 +83,7 @@ func (b blockWriter) Write(data []byte) (int, error) {
 		total += n
 		b.e.buf[0] = uint8(n)
 
-		n, b.e.err = b.e.w.Write(b.e.buf[:n+1])
+		_, b.e.err = b.e.w.Write(b.e.buf[:n+1])
 		if b.e.err != nil {
 			return 0, b.e.err
 		}