Running cratesfyi add-essential-files fails if nightly toolchain not installed

[rylev]

This happens due to check here which will bail out of the function if the check for the current version fails (which happens if the toolchain is not installed).

What's worse, because nothing is logged the user is not told about this error at all. It returns a generic error saying something failed.

Ideally, we would detect when the error is that the nightly toolchain is not installed, and we would install it.