Fix keybindings list being empty by default (#13456)

# Description

Made a mistake when fixing this for IR. The default behavior with no
options set is to list everything. Restored that.

This should go in the 0.96.1 patch release.

# Tests + Formatting
Added regression test.

crates/nu-cli/tests/commands/keybindings_list.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn not_empty() {
+    let result = nu!("keybindings list | is-not-empty");
+    assert_eq!(result.out, "true");
+}

crates/nu-cli/tests/commands/mod.rs

@@ -1 +1,2 @@
+mod keybindings_list;
 mod nu_highlight;