truncate offsets if those are greater than #messages

ISSUE:
```
W0721 22:07:01.569829 04252 logs.go:346] number of offsets for c279d63256b4:/opt/zenoss/log/central-query.log (numLines:6 numOffsets:10) is greater than number of lines: {"message":"INFO  2014-07-21 16:17:40,909 com.yammer.metrics.httpclient.InstrumentedHttpClient: Retrying request\nERROR 2014-07-21 16:17:42,044 org.zenoss.metrics.reporter.ZenossMetricsReporter: Error posting metrics\n! org.apache.http.client.HttpResponseException: Service Temporarily Unavailable\n! at org.apache.http.impl.client.BasicResponseHandler.handleResponse(BasicResponseHandler.java:68) ~central-query-0.0.7-SNAPSHOT.jar:na\n! at org.zenoss.metrics.reporter.HttpPoster$AuthResponseHandler.handleResponse(HttpPoster.java:117) ~central-query-0.0.7-SNAPSHOT.jar:na\n! at org.zenoss.metrics.reporter.HttpPoster$AuthResponseHandler.handleResponse(HttpPoster.java:112) ~central-query-0.0.7-SNAPSHOT.jar:na","@version":"1","@timestamp":"2014-07-21T18:26:55.884Z","file":"/opt/zenoss/log/central-query.log","host":"c279d63256b4","offset":["132663","132766","132871","132951","133089","133228","135276","135356","135494","135633"],"service":"4xmo6p334ds7l0h3qdf5cgm64","type":"centralquery","tags":["_grokparsefailure","multiline"],"loglevel":["ERROR","ERROR"],"logger":["org.zenoss.metrics.reporter.ZenossMetricsReporter","org.zenoss.metrics.reporter.ZenossMetricsReporter"]}
```