Fix review checkbox behavior in diff view

The saveReviewedState observer observes params.*, but should not set
reviewed state when view !== Gerrit.Nav.View.DIFF. This can (and did)
happen when the Gerrit.Nav API is used to change the view -- the
observer is triggered before the view is detached.

Bug: Issue 8192
Change-Id: I06c1875f6f515c0d001277e63eb7724728c85cba
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
index 364d844..24986ee 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js
@@ -605,8 +605,9 @@
       }
     },
 
-    _setReviewedObserver(_loggedIn) {
-      if (_loggedIn) {
+    _setReviewedObserver(_loggedIn, paramsRecord) {
+      const params = paramsRecord.base || {};
+      if (_loggedIn && params.view === Gerrit.Nav.View.DIFF) {
         this._setReviewed(true);
       }
     },