opening a large number of videos with vlc causes delay and unresponsive vlc

[Karl-Philipp Richter]

Steps to reproduce:

1. download a free MPlayer test file, like http://samples.mplayerhq.hu/MPEG-4/video.mp4 and move it into /tmp/a or similar
2. replicate it by running (requires a few GB of free space depending on the deduplication facilities of your filesystem)

```
import shutil
for i in range(0,1000):
    shutil.copy("/tmp/a/video.mp4", "/tmp/a/video-%d.mp4" % (i,))
```
3. open /tmp/a in nautilus, select all files and open them with VLC media player through the context menu

Instead of putting all files in the VLC queue like Ubuntu 17.04's nautilus did, an ~"opening in progress" dialog is opened blocking the UI for almost a minute while consuming 100% of all CPU cores. If the above is done during high memory consumption of another process hundreds of VLC processes are started and the display manager crashes (but that's another issues). If random playback is configured in VLC, it's ignored and always the last video is played first.

The is no apparent reason why multiple files cannot be opened like in 17.04.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: nautilus 1:3.26.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.13.0-21.24-generic 4.13.13
Uname: Linux 4.13.0-21-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.7-0ubuntu3.6
Architecture: amd64
CurrentDesktop: Unity:Unity7:ubuntu
Date: Fri Dec 22 01:06:27 2017
InstallationDate: Installed on 2015-12-12 (740 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: nautilus
UpgradeStatus: Upgraded to artful on 2017-10-19 (63 days ago)

[Sebastien Bacher (seb128)]

Looks like the same issue than bug #1772406