split: fix error msg shown if file doesn't exist

tests/by-util/test_split.rs

@@ -123,6 +123,15 @@ fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails().code_is(1);
 }
 
+#[test]
+fn test_split_non_existing_file() {
+    new_ucmd!()
+        .arg("non-existing")
+        .fails()
+        .code_is(1)
+        .stderr_is("split: cannot open 'non-existing' for reading: No such file or directory\n");
+}
+
 #[test]
 fn test_split_default() {
     let (at, mut ucmd) = at_and_ucmd!();