Only consider umu setup if there are files in .local/share/umu/

[CommandMC]

When umu starts downloading the runtime required for the specified tool, it will create a folder for it in UMU_LOCAL. If this download fails, the following code is supposed to catch the error, explain it, and stop the launch:

umu-launcher/umu/umu_run.py

Lines 888 to 894 in 24cdc86

	except HTTPError as e:
	if not has_umu_setup():
	err: str = (
	"umu has not been setup for the user\n"
	"An internet connection is required to setup umu"
	)
	raise RuntimeError(err)

However, has_umu_setup currently only checks whether there is any non-lock file/folder in UMU_LOCAL, meaning the empty runtime directory that was created gets found, and umu is considered "setup".

With this PR, we instead search for non-lock files (not folders) in UMU_LOCAL, which avoids the above issue

[R1kaB3rN]

For additional context, one case where an empty subdirectory in UMU_LOCAL can occur is when a new user is on a network that’s online but repo.steampowered.com is blacklisted.

[R1kaB3rN]

Recursively listing the contents from umu-launcher's base installation path can lead to a false negative in a session for users where a network errors occurs on runtime install, and there are multiple subdirectories (e.g., steamrt4) installed within umu-launcher's runtime installation path.

For example, if a client passes a Proton that requires a container runtime that hasn't been installed yet by umu-launcher, but during the installation process a network error had suddenly occurred.