About install node command

[Buguin]

Background
When I use "nvm install v19.0.0" to install Node, if the corresponding version of Node is not found in the repository, the file cannot be downloaded locally. However, the checksum is still verified.

Although a check was made using grep before the verification started, the nvm_compare_checksum function was still executed later. It is recommended to modify it to verify whether the downloaded file exists after downloading the file, and return if it does not exist. There is no need to execute the function further.

  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
  )

 # Check if the file is successfully downloaded, the previous "return 4" actually did not return
  if [ ! -f "${TARBALL}" ]; then
      nvm_err 'Download file not found, skip checksum.'
      return 7
  fi

  if nvm_grep '404 Not Found' "${TARBALL}" >/dev/null; then
    command rm -rf "${TARBALL}" "${tmpdir}"
    nvm_err "HTTP 404 at URL ${TARBALL_URL}"
    return 5
  fi

  nvm_compare_checksum "${TARBALL}" "${CHECKSUM}" || (
    command rm -rf "${tmpdir}/files"
    return 6
  )

[ljharb]

That sounds like a great improvement. Would you like to make a PR?