fix: refuse a hash scrape that reads no BIOS set

The MAME and FBNeo hash scrapers cached an empty parse for 24 hours and
reported OK. Both now raise before writing, and an empty cache is never
served as fresh.

scripts/scraper/fbneo_hash_scraper.py

@@ -42,6 +42,8 @@ def _is_cache_fresh() -> bool:
         return False
     try:
         data = json.loads(CACHE_PATH.read_text(encoding="utf-8"))
+        if not data.get("bios_sets"):
+            return False
         fetched_at = datetime.fromisoformat(data["fetched_at"])
         return datetime.now(timezone.utc) - fetched_at < timedelta(hours=STALE_HOURS)
     except (json.JSONDecodeError, KeyError, ValueError):
@@ -178,6 +180,10 @@ def fetch_and_cache(force: bool = False) -> dict[str, Any]:
 
         log.info("parsing source tree")
         bios_sets = parse_fbneo_source_tree(str(CLONE_DIR))
+        if not bios_sets or not commit:
+            # An empty read was cached for a day and merged nothing, and
+            # the pipeline step reported OK.
+            raise RuntimeError(f"no BIOS set read at FBNeo {version} ({commit[:12]})")
 
         cache: dict[str, Any] = {
             "source": "finalburnneo/FBNeo",