Prevent repeated db connect calls

Only call database.connect() if database.is_closed()
Prevents errors if _db_connect is triggered twice

frigate/http.py

@@ -47,6 +47,7 @@ def create_app(
 
     @app.before_request
     def _db_connect():
+        if database.is_closed():
             database.connect()
 
     @app.teardown_request