Check if code-review is part of permitted_labels

If code review is not part of permitted_labels, then trying to slice
undefined throws an error and the page doesn't load.

Change-Id: Ic9a1dadcef8c013cc10524a92d26857c20d62db8
diff --git a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
index 20fbc32..9473700 100644
--- a/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-actions/gr-change-actions.ts
@@ -954,7 +954,9 @@
     if (
       !result &&
       this.change.labels[CODE_REVIEW] &&
-      this._getLabelStatus(this.change.labels[CODE_REVIEW]) === LabelStatus.OK
+      this._getLabelStatus(this.change.labels[CODE_REVIEW]) ===
+        LabelStatus.OK &&
+      this.change.permitted_labels[CODE_REVIEW]
     ) {
       result = CODE_REVIEW;
     }