GHSA-w5g8-5849-vj76: NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion

NiceGUI's media file serving functions accept a user-controlled parameter that controls how files are read during streaming without checking if the parameter is valid. An attacker can use this to force the server to load entire files into memory at once instead of sending them in chunks (smaller pieces), which can cause the server to run out of memory and stop working, especially with large files like videos.