close-stream: make idemponent.

* stream.c (strm_base_init): Add new element to the initializer to
initialize the close_result member to nao, indicating that the close
operation has not been invoked.
(strm_base_mark): Mark the close_result value, if it isn't nao.
This is just in case it is a heap object. The structure delegate
mechanism opens the possibility that the stream is actually user code
that can return anything so we have to be careful.
(close_stream): Only call ops->close if close_result is nao, indicating
that close had never been called (or possibly that it had been called
bu threw an exception) and store the return value in close_result,
otherwise return the previously stored value.

* stream.h (struct strm_base): New member, close_result.

* txr.1: Documented.

0 files changed, 0 insertions, 0 deletions