[BUG] WebDAV connection test fails with 405 Method Not Allowed when using rclone webdav backend

[onlymash]

Describe the bug
When attempting to connect or test a WebDAV server hosted via rclone serve webdav, NextPlayer returns a 405 Method Not Allowed error.

To Reproduce
Steps to reproduce the behavior:

1. Set up an rclone serve webdav backend with --baseurl "/dav".
2. Configure & Test the WebDAV settings in NextPlayer
3. See error: Error contacting https://private.example.com:14433/dav (405 Method Not Allowed).

Expected behavior
The connection test should succeed, or handle trailing slashes for directory endpoints automatically.

Screenshots

Error contacting https://private.example.com:14433/dav (405 Method Not Allowed)

Device info (please complete the following information):

• Device: OnePlus 13
• Android version: 16
• App version: 0.17.4(71)

Additional context
Server Configuration (webdav.service)

[Unit]
Description=rclone webdav server
After=network-online.target remote-fs.target nss-lookup.target
Wants=network-online.target

[Service]
User=onlymash
Type=simple
LimitNOFILE=65535
ExecStart=rclone serve webdav /mnt \
        --addr :14433 \
        --baseurl "/dav" \
        --htpasswd /etc/nginx/.htpasswd \
        --cert /etc/ssl/private.example.com/fullchain.pem \
        --key /etc/ssl/private.example.com/key.pem \
        --transfers 8 \
        --checkers 8 \
        --vfs-cache-mode writes \
        --vfs-read-chunk-size 64M \
        --vfs-read-chunk-size-limit off \
        --buffer-size 128M \
        --no-checksum \
        --no-modtime
Restart=always

[Install]
WantedBy=multi-user.target