[Windows] If Streamlink Twitch GUI is already running, it throws an error during setup to update

[Porkepix]

Bug report

• I understand the difference between Streamlink and Streamlink Twitch GUI.
• This is a bug report and I have read the contribution guidelines.

Environment details

Operating system and version:
Windows 7

Streamlink Twitch GUI version:
1.8.1

Description

Streamlink twitch gui detects an update, you go to download it and run the setup and it failes as user didn't close the application, throwing an I/O error on a dll.

Expected / Actual behavior

The setup could detect the application is running and offer to close it.

Reproduction steps

Run application setup while having it already running.

[bastimeyer]

The Windows installer already tries to kill the main process of STG if it is still running:

1. Kill command definition
   1.1. taskkill command documentation
   1.2. Variables used by the installer template
   1.3. Grunt config
   1.4. package.json (package field)
   1.5. main.json (main field)
2. Command logging and execution at the beginning of the install section

I'm not sure if something has changed recently, or if it's just unreliable (I'd not be surprised), but it was working correctly when I implemented it. I haven't checked it since then though.

If you're having a better idea/solution on how to implement this, please send a pull request.