BatchUpdate: Always bump rowVersion when dirty

When any Op returns true from updateChange, we need to bump the
rowVersion so we get a new ETag.

Add a regression test based on PostReviewers, which was the
manifestation reported by one of our internal users.

Change-Id: Ibe1e69430e2e24b5bcbb85cb24a032d820fdd10e

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

@@ -589,26 +589,23 @@ public class BatchUpdate implements AutoCloseable {
           for (Op op : e.getValue()) {
             dirty |= op.updateChange(ctx);
           }
-          ctx.getChange().setLastUpdatedOn(ctx.getWhen());
-          Iterable<Change> changes = Collections.singleton(ctx.getChange());
+          if (!dirty) {
+            return;
+          }
           if (newChanges.containsKey(id)) {
-            db.changes().insert(changes);
+            db.changes().insert(bumpLastUpdatedOn(ctx));
           } else if (ctx.saved) {
-            db.changes().update(changes);
+            db.changes().update(bumpLastUpdatedOn(ctx));
           } else if (ctx.deleted) {
-            db.changes().delete(changes);
-          }
-          if (dirty) {
-            db.commit();
+            db.changes().delete(bumpLastUpdatedOn(ctx));
+          } else {
+            db.changes().update(bumpRowVersionNotLastUpdatedOn(ctx));
           }
+          db.commit();
         } finally {
           db.rollback();
         }
 
-        if (!dirty) {
-          return;
-        }
-
         if (ctx.deleted) {
           if (notesMigration.writeChanges()) {
             new ChangeDelete(plcUtil, getRepository(), ctx.getNotes()).delete();
@@ -636,6 +633,17 @@ public class BatchUpdate implements AutoCloseable {
     }
   }
 
+  private static Iterable<Change> bumpLastUpdatedOn(ChangeContext ctx) {
+    Change c = ctx.getChange();
+    c.setLastUpdatedOn(ctx.getWhen());
+    return Collections.singleton(c);
+  }
+
+  private static Iterable<Change> bumpRowVersionNotLastUpdatedOn(
+      ChangeContext ctx) {
+    return Collections.singleton(ctx.getChange());
+  }
+
   private ChangeContext newChangeContext(Change.Id id) throws Exception {
     Change c = newChanges.get(id);
     if (c == null) {