style: add component 'rule' for horizontal file delimiter

tests/integration_tests.rs

@@ -570,6 +570,18 @@ fn empty_file_leads_to_empty_output_with_grid_enabled() {
         .stdout("");
 }
 
+#[test]
+fn empty_file_leads_to_empty_output_with_rule_enabled() {
+    bat()
+        .arg("empty.txt")
+        .arg("--style=rule")
+        .arg("--decorations=always")
+        .arg("--terminal-width=80")
+        .assert()
+        .success()
+        .stdout("");
+}
+
 #[test]
 fn filename_basic() {
     bat()