Fix: Wrong ps/rev in change-merged stream-event

When using cherry-pick as merge strategy, the wrong ref was
display in the change-merged stream-event.

The issue stems from Gerrit would not acknowledge the
resulting new pachset (the actual cherry-pick).

Change-Id: I67ecfd33c584e870e0865e18c759a479ec4a595a

gerrit-server/src/main/java/com/google/gerrit/server/git/MergeOp.java

@@ -900,6 +900,7 @@ public class MergeOp {
 
     final ObjectId id = commit(m, mergeCommit);
     final CodeReviewCommit newCommit = (CodeReviewCommit) rw.parseCommit(id);
+    final Change oldChange = n.change;
 
     n.change =
         db.changes().atomicUpdate(n.change.getId(),
@@ -929,6 +930,9 @@ public class MergeOp {
               }
             });
 
+    this.submitted.remove(oldChange);
+    this.submitted.add(n.change);
+
     if (approvalList != null) {
       for (PatchSetApproval a : approvalList) {
         db.patchSetApprovals().insert(