cloud tier: s3 consume all read response body

fix https://github.com/seaweedfs/seaweedfs/issues/3584

weed/storage/backend/s3_backend/s3_backend.go

@@ -124,8 +124,6 @@ func (s3backendStorageFile S3BackendStorageFile) ReadAt(p []byte, off int64) (n
 
 	bytesRange := fmt.Sprintf("bytes=%d-%d", off, off+int64(len(p))-1)
 
-	// glog.V(0).Infof("read %s %s", s3backendStorageFile.key, bytesRange)
-
 	getObjectOutput, getObjectErr := s3backendStorageFile.backendStorage.conn.GetObject(&s3.GetObjectInput{
 		Bucket: &s3backendStorageFile.backendStorage.bucket,
 		Key:    &s3backendStorageFile.key,
@@ -137,13 +135,16 @@ func (s3backendStorageFile S3BackendStorageFile) ReadAt(p []byte, off int64) (n
 	}
 	defer getObjectOutput.Body.Close()
 
-	glog.V(4).Infof("read %s %s", s3backendStorageFile.key, bytesRange)
-	glog.V(4).Infof("content range: %s, contentLength: %d", *getObjectOutput.ContentRange, *getObjectOutput.ContentLength)
+	// glog.V(3).Infof("read %s %s", s3backendStorageFile.key, bytesRange)
+	// glog.V(3).Infof("content range: %s, contentLength: %d", *getObjectOutput.ContentRange, *getObjectOutput.ContentLength)
 
+	var readCount int
 	for {
-		if n, err = getObjectOutput.Body.Read(p); err == nil && n < len(p) {
-			p = p[n:]
-		} else {
+		p = p[readCount:]
+		readCount, err = getObjectOutput.Body.Read(p)
+		n += readCount
+
+		if err != nil {
 			break
 		}
 	}