Opening MTP Android device fails with "the location is not a folder" while gvfs mount is healthy

Description

Clicking an Android phone (connected via USB in MTP / File Transfer mode) from Nemo's sidebar or "Devices" view produces the error "the location is not a folder". The device's mtp:// URI fails to open as a browsable folder in Nemo, even though the gvfs MTP backend has successfully mounted the device.

Environment

• Linux Mint 22.3 (Cinnamon), Ubuntu 24.04 base
• Nemo: 6.6.3
• gvfs-backends: 1.54.4-0ubuntu1~24.04.2
• gvfs-fuse: 1.54.4-0ubuntu1~24.04.2
• libmtp9t64: 1.1.21-3.1ubuntu1

Device

• Samsung Galaxy phone, Android 16, connected via USB, "File transfer (MTP)" mode selected
• USB ID: 04e8:6860 (Samsung Galaxy series, MTP mode)

Steps to reproduce

1. Connect Android phone via USB.
2. On the phone, select "File transfer / Android Auto" USB mode.
3. In Nemo, click the phone entry in the sidebar (or the "SAMSUNG Android" volume).

Expected behavior

Nemo opens the phone's storage and lists its top-level folders (DCIM, Download, etc.).

Actual behavior

Nemo shows: "the location is not a folder" and does not browse into the device.

Diagnostic evidence the mount is actually healthy

`gio mount -li` reports:
```
Volume(0): SAMSUNG Android
Type: GProxyVolume (GProxyVolumeMonitorMTP)
activation_root=mtp://SAMSUNG_SAMSUNG_Android_/
Mount: mtp -> mtp://SAMSUNG_SAMSUNG_Android_/
```

And the FUSE path is fully browsable:
```
$ ls "/run/user/1000/gvfs/mtp:host=SAMSUNG_SAMSUNG_Android_/"
Internal storage
```

Workaround

Opening the FUSE path directly works:
```
nemo "/run/user/1000/gvfs/mtp:host=/Internal storage"
```

So the gvfs MTP mount itself is fine — the issue appears to be in how Nemo navigates `mtp://` URIs from the sidebar/device entry.

Additional notes

• Not covered by existing issues #2734, #2663, or #3474 (those describe mount failures or segfaults — here the mount succeeds).
• Related but distinct from #3291 (preview with MTP).

Start by tracing Nemo's sidebar and Devices-view activation path for the reported mtp:// URI, then compare it with the working FUSE path shown in the issue. Reproduce with an MTP device and confirm that selecting the device opens its storage and lists top-level folders such as DCIM and Download instead of reporting that the location is not a folder.