Plugins can't handle csharpier not installing correctly to the custom location

[belav]

See #682

java.io.IOException: Cannot run program "/Users/fredrikwallen/.cache/csharpier/0.17.0/dotnet-csharpier": error=2, No such file or directory

I believe the problem is that the directory /Users/fredrikwallen/.cache/csharpier/0.17.0 is empty, possibly because csharpier failed to install.

The plugins should detect this condition. Ideally they would recover from it. If they can't recover, they should notify the user.