nvm_install_binary
-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.
$_
nvm.sh
nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` to detect its source location. Adding `: nvm.sh` before each source line ensures `$_` is set correctly, preventing breakage when the previous command (e.g., `set -ex`) overwrites it.
install
Fixes #2114.