[Fix] `nvm_install_binary`: return failure when binary download fails with `-b`

When `nosource=1` (the `-b` flag) and binary download fails, the function returned 0 (success) instead of a non-zero exit code, masking the installation failure.

Bug introduced in https://github.com/nvm-sh/nvm/commit/4fdef427e4b1d563570ba5992bdbe7d7e23f025b / #2439.