RebuildNoteDb: Actually throw when NoteDb writes are disabled

The die method returns an exception, which we were never throwing.
Proceeding with writes disabled has the effect in NoteDbUpdateManager
of short-circuiting and not doing any work.

Change-Id: Ib0c3d5c7a40d6b4ab2205e690e6d5d32feb9fac0
diff --git a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/RebuildNoteDb.java b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/RebuildNoteDb.java
index ae4a429..ed05786 100644
--- a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/RebuildNoteDb.java
+++ b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/RebuildNoteDb.java
@@ -120,7 +120,7 @@
     sysInjector = createSysInjector();
     sysInjector.injectMembers(this);
     if (!notesMigration.enabled()) {
-      die("NoteDb is not enabled.");
+      throw die("NoteDb is not enabled.");
     }
     LifecycleManager sysManager = new LifecycleManager();
     sysManager.add(sysInjector);