nixos-install: quote nixos-prepare-root arguments

This prevents the script from breaking when channel_root is empty.

Changed files
+1 -1
nixos
modules
installer
+1 -1
nixos/modules/installer/tools/nixos-install.sh
···
nix-store --export $channel_root > $channel_closure
# Populate the target root directory with the basics
-
@prepare_root@/bin/nixos-prepare-root $mountPoint $channel_root $system_root @nixClosure@ $system_closure $channel_closure
+
@prepare_root@/bin/nixos-prepare-root "$mountPoint" "$channel_root" "$system_root" @nixClosure@ "$system_closure" "$channel_closure"
# nixos-prepare-root doesn't currently do anything with file ownership, so we set it up here instead
chown @root_uid@:@nixbld_gid@ $mountPoint/nix/store