Retain unsaved drafts in comments model

Unsaved drafts are drafts which do not have an id associated with them
yet.
Adding the newly created drafts to the model triggered the observer
"computeFileThreads" in gr-diff-host which eventually called
createCommentThreads in comment-util which required additional
handling for comments without an id.

Bug: Issue 14828
Change-Id: I685d8ea5ee94ac6e5b84f9c01065dfea8c730927
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
index 6c96e34..a7879f4 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.js
@@ -26,6 +26,7 @@
 import {CoverageType} from '../../../types/types.js';
 import {addListenerForTest, stubRestApi} from '../../../test/test-utils.js';
 import {EditPatchSetNum, ParentPatchSetNum} from '../../../types/common.js';
+import {_testOnly_resetState} from '../../../services/comments/comments-model.js';
 
 const basicFixture = fixtureFromElement('gr-diff-host');
 
@@ -42,6 +43,7 @@
     element.path = 'some/path';
     sinon.stub(element.reporting, 'time');
     sinon.stub(element.reporting, 'timeEnd');
+    _testOnly_resetState();
     await flush();
   });