Fix Corral File Wait

[caliskanugur]

After the concurrent updates for the corral, the wait makes sure the file exists, but it's missing a nil value which is the return value if the file doesn't exist

03:12:15 �[31mERRO�[0m[0254] error getting the bootstrap password: GetCorralEnvVar: time="2024-10-28T07:12:04Z" level=fatal msg="open /root/.corral/corrals/rancherha/corral.yaml: no such file or directory"