Fixes possible issue with no-op creator.

Leaving a no-op CREATOR can lead to issues. We throw a run-time
exception to prevent anyone from using this. The StatsLogEventWrapper is
meant to be write-only since it's only used to send data to statsd.

Bug: 112550251
Test: Tested with provided POC app by external researcher.
Change-Id: I001d84e2a61a1cd8a4f59aa156ca52f73ad0f6e1