avio: Handle AVERROR_EOF in the same way as the return value 0

This makes sure the ffurl_read_complete function actually
returns the number of bytes read, as the documentation of the
function says, even if the underlying protocol uses AVERROR_EOF
instead of 0.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/avio.c

@@ -238,7 +238,7 @@ static inline int retry_transfer_wrapper(URLContext *h, unsigned char *buf, int
             else
                 av_usleep(1000);
         } else if (ret < 1)
-            return ret < 0 ? ret : len;
+            return (ret < 0 && ret != AVERROR_EOF) ? ret : len;
         if (ret)
            fast_retries = FFMAX(fast_retries, 2);
         len += ret;