fix: bug if z2jh is used as a dependency with an alias

[consideRatio]

If z2jh was used as a dependency helm chart, and it had an alias, this bug would happen which make template rendering fail.

As an example, the following Chart.yaml would cause an error.

apiVersion: v2
description: irrelevant
name: irrelevant
version: 0.1.0
dependencies:
  - name: jupyterhub
    version: "1.0.1"
    repository: "https://jupyterhub.github.io/helm-chart"
    alias: dep-chart-alias

executing "jupyterhub.fullname" at <.Values.jupyterhub.fullnameOverride>: nil pointer evaluating interface {}.fullnameOverride