Fix chunked data bug in embedded version of WsgiDAV (affects big files, as well as all files from some dav clients)

[aleqx]

Fixes: https://github.com/haiwen/seafile/issues/2723#issuecomment-1905295963

Description: The currently embedded version of WsgiDAV is 4.1.0 which has a bug for chunked data. This PR fixes the problem for the embedded WsgiDAV. This is an instant drop-in replacement, so it's instant to incorporate. Upgrading WsgiDAV to 4.3.0 (which does fix the bug) may braek compatibility with the existing Seafile integration so devs may need more time before making that upgrade.