Unable to compare remote folder (mounted to /run/user/1000/gvfs) and local folder

Steps to reproduce:
1. Connect to some share with Caja (enter sftp://<email address hidden> in the address-bar), so get the folder mounted to /run/user/1000/gvfs/sftp:host=hostname.local,user=user/
2. Open terminal and run Meld from it to compare folder pair:

```
meld /run/user/1000/gvfs/sftp:host=hostname.local,user=user/home/user/Desktop ~/Desktop
```

Expected results:

* Meld opens with comparison of two folders

Actual results:

* Meld shows the error in the terminal

```
$ meld /run/user/1000/gvfs/sftp:host=hostname.local,user=user/home/user/Desktop ~/Desktop
Usage:
  meld Start with an empty window
  meld <file|folder> Start a version control comparison
  meld <file> <file> [<file>] Start a 2- or 3-way file comparison
  meld <folder> <folder> [<folder>] Start a 2- or 3-way folder comparison

Error: remote folder “/run/user/1000/gvfs/sftp:host=hostname.local,user=user/home/user/Desktop” not supported

```

and do not open comparison window.

Note: this method works normally on 16.04 LTS and on 18.04 LTS, but not on 19.10 and 20.04 LTS.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: meld 3.20.2-1ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-18.22-generic 5.4.24
Uname: Linux 5.4.0-18-generic x86_64
ApportVersion: 2.20.11-0ubuntu21
Architecture: amd64
CurrentDesktop: MATE
Date: Sat Mar 28 13:50:03 2020
InstallationDate: Installed on 2019-11-09 (139 days ago)
InstallationMedia: Ubuntu-MATE 19.10 "Eoan Ermine" - Release amd64 (20191017)
PackageArchitecture: all
SourcePackage: meld
UpgradeStatus: Upgraded to focal on 2019-11-09 (139 days ago)