Fix crash on empty helm render: treat no-output chart as no-op

[Copilot]

When all chart templates are gated behind a falsy conditional, helm template --output-dir produces an empty directory. ReplaceWithRendered then crashed with an opaque assertion error because it expected exactly one subdirectory in the output dir.

Changes

• replace.go: After reading helmOutputDirEntries, if the slice is empty, remove the chart's content dirs (templates/, charts/, crds/) so subsequent helm processing also sees no resources, clean up the temp output dir, and return nil, nil (empty file list, no error). This is a no-op from the caller's perspective.

• testdata/charts/emptychart/: Minimal test chart with a ConfigMap template fully gated behind {{- if .Values.enabled }} (default: false).

• integration_test.go: New "empty render no op" integration test exercising this path via OverrideNamespace (which forces ReplaceWithRendered to be called).

Example

# templates/configmap.yaml — renders nothing by default
{{- if .Values.enabled }}
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-cm
{{- end }}

Previously, running chartify against such a chart (with any of OverrideNamespace, JsonPatches, StrategicMergePatches, or Transformers configured) would crash:

assertion failed: unexpected dir entry "" it must be the abs path to the output directory

After this fix, chartify returns successfully with an empty resource list.

• Fixes chartify crashes on empty render: expose sentinel error or treat as no-op #206