Fix RuneReader breaking right before EOF

bytes/regexp.go

@@ -35,10 +35,14 @@ func (rr *RuneReader) ReadRune() (r rune, size int, err error) {
 		rr.cursor = next
 		return 0, 0, fmt.Errorf("ReadRune: %w", err)
 	}
+	if n == 0 {
+		return 0, 0, io.EOF
+	}
 	s = s[:n]
+	fmt.Println("read bytes:", s)
 	r, size = utf8.DecodeRune(s)
 	rr.cursor = rr.cursor.At(rr.cursor.Pos() + uint64(size))
-	return r, size, err
+	return r, size, nil
 }
 
 func (rr *RuneReader) Cursor() cursor.Cursor[byte] {