Skip checksum when download file failed.

[Buguin]

Fixes #3075 Check if the file is successfully downloaded

[freddyg11]

Ÿ

[ljharb]

@Buguin are you still interested in completing this PR?

[Buguin]

@Buguin are you still interested in completing this PR?

Sorry，I'm too busy working this time. Recently, I will make a push to solve the problem of not being able to return when an error is reported in the following code.

nvm_err "Downloading ${TARBALL_URL}..."
  nvm_download -L -C - "${PROGRESS_BAR}" "${TARBALL_URL}" -o "${TARBALL}" || (
    command rm -rf "${TARBALL}" "${tmpdir}"
    nvm_err "Binary download from ${TARBALL_URL} failed, trying source."
    return 4---it does not work, function not return.
  )

[Buguin]

@Buguin are you still interested in completing this PR?

I have transformed nvm_download_artifact function, which allows you to determine the download status based on the execution results.

[ljharb]

I've rebased this, but it still needs tests. @Buguin any chance you're still interesting in completing this PR?