fix(chart): all in one maxVolumes value (#8683)

* fix(chart): all-in-one deployment maxVolumes value

* chore(chart): improve readability

* fix(chart): maxVolume nil value check

* fix(chart): guard against nil/empty volume.dataDirs before calling first

Without this check, `first` errors when volume.dataDirs is nil or empty,
causing a template render failure for users who omit the setting entirely.

---------

Co-authored-by: Copilot <copilot@github.com>

k8s/charts/seaweedfs/templates/all-in-one/all-in-one-deployment.yaml

@@ -168,8 +168,12 @@ spec:
               {{- if .Values.allInOne.disableHttp }}
               -disableHttp={{ .Values.allInOne.disableHttp }} \
               {{- end }}
-              {{- if and (.Values.volume.dataDirs) (index .Values.volume.dataDirs 0 "maxVolumes") }}
-              -volume.max={{ index .Values.volume.dataDirs 0 "maxVolumes" }} \
+              {{- if .Values.volume.dataDirs }}
+              {{- with (first .Values.volume.dataDirs) }}
+              {{- if and (hasKey . "maxVolumes") (ne .maxVolumes nil) }}
+              -volume.max={{ .maxVolumes }} \
+              {{- end }}
+              {{- end }}
               {{- end }}
               -master.port={{ .Values.master.port }} \
               {{- if .Values.global.enableReplication }}