ChangeUpdate: fix comparison of Change.Id to Change.Key

Fix comparison of Change.Id to Change.Key in ChangeUpdate.

Commit 6761264d0848163ab48695e2edcb661a74137d9f already fixed the
same problem in ChangeInserter.

Both problems were being reported by FindBugs:

  Call to com.google.gerrit.reviewdb.client.Change$Id.equals(
  com.google.gerrit.reviewdb.client.Change$Key) in
  com.google.gerrit.server.notedb.ChangeUpdate.setPatchSetId(
  PatchSet$Id)

  This method calls equals(Object) on two references of different
  class types with no common subclasses. Therefore, the objects
  being compared are unlikely to be members of the same class at
  runtime (unless some application classes were not analyzed, or
  dynamic class loading can occur at runtime). According to the
  contract of equals(), objects of different classes should always
  compare as unequal; therefore, according to the contract defined
  by java.lang.Object.equals(Object), the result of this comparison
  will always be false at runtime.

Change-Id: I75f833d1c19f83abdddd765010416d5de6fffec3
1 file changed