Fix bug in lrf-meta that could cause corrupted LRF files when setting metadata.

src/calibre/ebooks/lrf/meta.py

@@ -375,6 +375,7 @@ class LRFMetaFile(object):
             delta = insert_into_file(self._file, stream, self.info_start, \
                                      self.info_start + orig_size - 4)
             
+            if self.toc_object_offset > 0:
                 self.toc_object_offset   += delta
             self.object_index_offset += delta
             self.update_object_offsets(delta)
@@ -685,3 +686,4 @@ def main(args=sys.argv):
         
 if __name__ == '__main__':
     sys.exit(main())
+