[#98] fstree: Do not fail iteration over just removed files

A directory is read and files are saved to a local variable. The iteration
over such files may lead to a non-existing files reading due to a normal SN
operation cycle and, therefore, may lead to a returning the OS error to a
caller. Skip just removed (or lost) files as the golang std library does in
similar situations:
5f1a0320b9/src/os/dir_unix.go (L128-L133).

Signed-off-by: Pavel Karpy <p.karpy@yadro.com>

CHANGELOG.md

@@ -50,6 +50,7 @@ Changelog for FrostFS Node
 - Actually use `object.put.pool_size_local` and independent pool for local puts (#64).
 - Pretty printer of basic ACL in the NeoFS CLI (#2259)
 - Adding of public key for nns group `group.frostfs` at init step (#130)
+- Iterating over just removed files by FSTree (#98)
 
 ### Removed
 ### Updated

pkg/local_object_storage/blobstor/fstree/fstree.go

@@ -135,13 +135,16 @@ func (t *FSTree) iterate(depth uint64, curPath []string, prm common.IteratePrm)
 			continue
 		}
 
+		data, err := os.ReadFile(filepath.Join(curPath...))
+		if err != nil && os.IsNotExist(err) {
+			continue
+		}
+
 		if prm.LazyHandler != nil {
 			err = prm.LazyHandler(addr, func() ([]byte, error) {
-				return os.ReadFile(filepath.Join(curPath...))
+				return data, err
 			})
 		} else {
-			var data []byte
-			data, err = os.ReadFile(filepath.Join(curPath...))
 			if err == nil {
 				data, err = t.Decompress(data)
 			}