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

## What does this PR do?

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

## Why is it important?

The offset could be incorrect if Filebeat skips the line if the line should not be published because of user configuration in `export_line` or `import_line`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

CHANGELOG.next.asciidoc

@@ -271,6 +271,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix CredentialsJSON unpacking for `gcp-pubsub` and `httpjson` inputs. {pull}23277[23277]
 - Change the `event.created` in Netflow events to be the time the event was created by Filebeat
   to be consistent with ECS. {pull}23094[23094]
+- Update `filestream` reader offset when a line is skipped. {pull}23417[23417]
 
 *Filebeat*
 

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
 		}