Use is None guards for uptime and fxcount; fix outdated comment

Treat fxcount=0 as a valid value rather than "missing": change
`not fxcount` to `fxcount is None` in _check_effects_changed, consistent
with the earlier uptime fix. A device reporting zero effects would
otherwise be forced into a safe-refetch loop on every poll.

Update the inline comment in test_update_skips_presets_when_unchanged
to reflect that the first update now fetches three endpoints
(/json, /json/effects, /presets.json) after mock_json_and_presets
was extended to also stub /json/effects.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mik-laj

src/wled/wled.py

@@ -873,9 +873,9 @@ def _check_effects_changed(
             return (False, self._effects_version)
 
         info = data["info"]
-        if (uptime := info.get("uptime")) is None or not (
+        if (uptime := info.get("uptime")) is None or (
             fxcount := info.get("fxcount")
-        ):
+        ) is None:
             return (True, None)
 
         try:

tests/test_wled.py

@@ -279,7 +279,7 @@ async def test_update_skips_presets_when_unchanged(
     """Test update() skips fetching presets.json when presets haven't changed."""
     wled_data = load_fixture_json("wled")
 
-    # First update: fetches both /json and /presets.json
+    # First update: fetches /json, /json/effects, /presets.json
     responses.get(
         "http://example.com/json",
         status=200,