[#142] Fix multipart-objects download

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

internal/service/frostfs/multi_object_reader.go

@@ -172,12 +172,15 @@ func findEndPart(cfg MultiObjectReaderConfig) (index int, length uint64) {
 func (x *MultiObjectReader) Read(p []byte) (n int, err error) {
 	if x.curReader != nil {
 		n, err = x.curReader.Read(p)
+		if err != nil {
+			if err := x.curReader.Close(); err != nil {
+				return n, err
+			}
+		}
 		if !errors.Is(err, io.EOF) {
 			return n, err
 		}
-		if err = x.curReader.Close(); err != nil {
-			return n, err
-		}
+
 		x.curIndex++
 	}