Fix empty delays in script helper (#114346)

fixes
```
Logger: homeassistant.components.automation.kamermaster_knop_4_acties_licht
Bron: components/automation/__init__.py:726
integratie: Automatisering (documentatie, problemen)
Eerst voorgekomen: 22:17:29 (5 gebeurtenissen)
Laatst gelogd: 22:59:24

While executing automation automation.kamermaster_knop_4_acties_licht
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/automation/__init__.py", line 726, in async_trigger
    return await self.action_script.async_run(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 1645, in async_run
    return await asyncio.shield(create_eager_task(run.async_run()))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 454, in async_run
    await self._async_step(log_exceptions=False)
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 506, in _async_step
    self._handle_exception(
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 536, in _handle_exception
    raise exception
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 504, in _async_step
    await getattr(self, handler)()
  File "/usr/src/homeassistant/homeassistant/helpers/script.py", line 626, in _async_delay_step
    if timeout_future.done():
       ^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'done'
```

homeassistant/helpers/script.py

@@ -615,6 +615,11 @@ class _ScriptRun:
 
         delay = delay_delta.total_seconds()
         self._changed()
+        if not delay:
+            # Handle an empty delay
+            trace_set_result(delay=delay, done=True)
+            return
+
         trace_set_result(delay=delay, done=False)
         futures, timeout_handle, timeout_future = self._async_futures_with_timeout(
             delay

tests/helpers/test_script.py

@@ -672,6 +672,31 @@ async def test_delay_basic(hass: HomeAssistant) -> None:
     )
 
 
+async def test_empty_delay(hass: HomeAssistant) -> None:
+    """Test an empty delay."""
+    delay_alias = "delay step"
+    sequence = cv.SCRIPT_SCHEMA({"delay": {"seconds": 0}, "alias": delay_alias})
+    script_obj = script.Script(hass, sequence, "Test Name", "test_domain")
+    delay_started_flag = async_watch_for_action(script_obj, delay_alias)
+
+    try:
+        await script_obj.async_run(context=Context())
+        await asyncio.wait_for(delay_started_flag.wait(), 1)
+    except (AssertionError, TimeoutError):
+        await script_obj.async_stop()
+        raise
+    else:
+        await hass.async_block_till_done()
+        assert not script_obj.is_running
+        assert script_obj.last_action is None
+
+    assert_action_trace(
+        {
+            "0": [{"result": {"delay": 0.0, "done": True}}],
+        }
+    )
+
+
 async def test_multiple_runs_delay(hass: HomeAssistant) -> None:
     """Test multiple runs with delay in script."""
     event = "test_event"