Update filestream reader offset when line is skipped (elastic#23417)

This PR adds two previously missing offset updates to the `filestream` reader when a line is skipped.

The offset could be incorrect if Filebeat skips the line if the line should not be published because of user configuration in `export_line` or `import_line`

If the offset is not updated in the reader, the state information of newer published events become incorrect. This might lead to duplicated events if Filebeat is restarted.

(cherry picked from commit e5cd64f)

CHANGELOG.next.asciidoc

@@ -187,6 +187,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 *Filebeat*
 
+- Update `filestream` reader offset when a line is skipped. {pull}23417[23417]
 - cisco/asa fileset: Fix parsing of 302021 message code. {pull}14519[14519]
 - Fix filebeat azure dashboards, event category should be `Alert`. {pull}14668[14668]
 - Fixed dashboard for Cisco ASA Firewall. {issue}15420[15420] {pull}15553[15553]

filebeat/input/filestream/input.go

@@ -318,13 +318,13 @@ func (inp *filestream) readFromSource(
 			return nil
 		}
 
+		s.Offset += int64(message.Bytes)
+
 		if message.IsEmpty() || inp.isDroppedLine(log, string(message.Content)) {
 			continue
 		}
 
 		event := inp.eventFromMessage(message, path)
-		s.Offset += int64(message.Bytes)
-
 		if err := p.Publish(event, s); err != nil {
 			return err
 		}