Incorrect error message when a sub-configuration file is not found

[WillHutt]

My selene.toml contained:

std = "roblox+testez"

When I run selene I get this output here on v0.13:

$ selene src/
`std = "roblox"`, but there is no roblox.toml in this directory. We are automatically generating one for you now!
By the way, you can do this manually in the future if you need to use new Roblox features with: `selene generate-roblox-std`.
ERROR: Even after generating the `roblox` standard library, we couldn't retrieve the standard library: io error: The system cannot find the file specified. (os error 2)

The roblox.toml was present and generated correctly. It was actually not able to find the testez.toml. The error message should have specifically said testez and not roblox.