BytesObjectInput skip with negative uses offset incorrectly

I noticed that ServerEventLoggerTest would fail intermittently as in http://ci.infinispan.org/viewLog.html?buildId=44854&tab=buildResultsDiv&buildTypeId=bt9&logTab=#testNameId2739787854537371844

This is caused by the fact that offset is used incorrectly when resetting the BytesObjectInput.