close mkstemp fd before reopening file in _tempfilepager

[bysiber]

_tempfilepager creates a temporary file using tempfile.mkstemp(), which returns an open file descriptor. However, the file is then re-opened via open_stream(filename, "wb") for writing without closing the original fd first.

The original fd stays open for the duration of the write and the entire subprocess call, only being closed in the finally block. This is a resource leak and can cause issues on Windows where open file descriptors prevent other processes from accessing the file — the pager subprocess may not be able to read the temp file.

This moves the os.close(fd) call to immediately after mkstemp(), before the file is re-opened for writing.