Fix buffer flushing to work with tei2korapxml

Change-Id: I54eef64bea40f4ebb528e7f9870b9277000a4c13
diff --git a/token_writer.go b/token_writer.go
index bccb1bd..39d97fa 100644
--- a/token_writer.go
+++ b/token_writer.go
@@ -106,6 +106,7 @@
 	} else if flags&SENTENCES != 0 {
 		tw.SentenceEnd = func(_ int) {
 			writer.WriteByte('\n')
+			writer.Flush()
 		}
 
 		// Ignore sentence boundaries
@@ -116,7 +117,6 @@
 	// Write token or sentence positions
 	if flags&(TOKEN_POS|SENTENCE_POS) != 0 {
 		tw.TextEnd = func(_ int) {
-			writer.Flush()
 
 			// Write token positions
 			if flags&TOKEN_POS != 0 {
@@ -140,6 +140,8 @@
 				sentB = true
 			}
 
+			writer.Flush()
+
 			posC = 0
 			pos = pos[:0]
 		}