Ignore symlinks with missing target, add better backup logging, update copyright year to 2021

server/filesystem/archive.go

@@ -152,7 +152,12 @@ func (a *Archive) addToArchive(p string, rp string, w *tar.Writer) error {
 	if s.Mode()&os.ModeSymlink != 0 {
 		// Read the target of the symlink.
 		target, err = os.Readlink(s.Name())
-		if err != nil && !os.IsNotExist(err) {
+		if err != nil {
+			// Skip symlinks if the target does not exist.
+			if os.IsNotExist(err) {
+				return nil
+			}
+
 			return errors.WithMessagef(err, "failed to read symlink target for '%s'", rp)
 		}
 	}