ChangeData: Clear currentPatchSet in setPatchSets

currentPatchSet is lazily loaded from the list of all patch sets. If
that list changes, currentPatchSet should change as well. Add a small
regression test.

Change-Id: I63eb44bcf92b9b7d3993941519c0ac80db60d5fb

gerrit-server/src/main/java/com/google/gerrit/server/query/change/ChangeData.java

@@ -450,6 +450,10 @@ public class ChangeData {
     return change;
   }
 
+  public void setChange(Change c) {
+    change = c;
+  }
+
   public Change reloadChange() throws OrmException {
     change = db.changes().get(legacyId);
     return change;
@@ -545,6 +549,7 @@ public class ChangeData {
   }
 
   public void setPatchSets(Collection<PatchSet> patchSets) {
+    this.currentPatchSet = null;
     this.patchSets = patchSets;
   }