Fix nil check in rejectBySize

cmd/restic/exclude.go

@@ -301,6 +301,10 @@ func rejectBySize(maxSizeStr string) (RejectFunc, error) {
 	}
 
 	return func(item string, fi os.FileInfo) bool {
+		if fi == nil {
+			return false
+		}
+
 		// directory will be ignored
 		if fi.IsDir() {
 			return false