Fix error logging only working when running as administrator

[VikeMK]

When LiveSplit does not have access to create or read Event Logs, EventLog.SourceExists will throw an exception. So what was happening was that the creation of the event source failed, but the trace listener was still added. Then, every time a trace was made it would throw an exception because it didn't have access to the event log. This works when running as administrator, but fails otherwise.