Fix SIGSEGV in S3StorageInteractor.ListPath. (#66)

When source S3 bucket have been deleted we receive SignatureDoesNotMatch error when trying to
list objects in bucket. This error wasn't handled properly, so it lead to nil-reference dereference
in next line. (Also, yp-client showed `failed to read params: EOF` to client)

pkg/proc/interaction.go

@@ -121,7 +121,7 @@ func ProcessPutExtended(
 					return
 				} else if n != int(msg.Sz) {
 
-					_ = ycl.ReplyError(fmt.Errorf("unfull write"), "failed to compelete request")
+					_ = ycl.ReplyError(fmt.Errorf("unfull write"), "failed to complete request")
 
 					return
 				}
@@ -177,7 +177,7 @@ func ProcessListExtended(msg message.ListMessage, s storage.StorageInteractor, c
 
 	objectMetas, err := s.ListPath(msg.Prefix)
 	if err != nil {
-		_ = ycl.ReplyError(fmt.Errorf("could not list objects: %s", err), "failed to compelete request")
+		_ = ycl.ReplyError(fmt.Errorf("could not list objects: %s", err), "failed to complete request")
 
 		return nil
 	}

pkg/storage/s3storage.go

@@ -166,6 +166,7 @@ func (s *S3StorageInteractor) ListPath(prefix string) ([]*object.ObjectInfo, err
 		out, err := sess.ListObjectsV2(input)
 		if err != nil {
 			fmt.Printf("list error: %v\n", err)
+			return nil, err
 		}
 
 		for _, obj := range out.Contents {