Ignore anonymous userdata folder

[DareFox]

The app crashes when trying to read anonymous user config file, 'cause it doesn't have required PersonaName field

Loading overlays...
Loaded 6 overlays. 

You can find many user-created overlays at https://www.reddit.com/r/steamgrid/wiki/overlays .

Looking for Steam directory...
If SteamGrid doesn´t find the directory automatically, launch it with an argument linking to the Steam directory.
Loading users...
Setting permission...
Setting permission...
Setting permission...
panic: runtime error: index out of range [1] with length 0

goroutine 1 [running]:
main.GetUsers({0x9c1aa60, 0x1a})
        C:/Users/BoppreH/Desktop/source/steamgrid/users.go:68 +0x66f
main.startApplication()
        C:/Users/BoppreH/Desktop/source/steamgrid/steamgrid.go:114 +0x13ff
main.main()
        C:/Users/BoppreH/Desktop/source/steamgrid/steamgrid.go:27 +0x44

Also, it doesn't make sense to fetch grids for anonymous user, since the only purpose for it is to download CLI game servers.

This PR adds a check to exclude anonymous folder from user parsing, and it should fix crash issue