gh-144067: Fix memory leak when initscr() follows setupterm()

[VanshAgarwal24036]

Calling setupterm() before initscr() can leak memory: setupterm()
allocates the global ncurses cur_term, and initscr() internally
reinitializes the terminal (via newterm()) without freeing the
existing cur_term.

This change frees an existing cur_term before calling initscr(),
preventing the leak observed under ASAN.

Note: the _curses module is not available on Windows, so this change
was not runtime-tested locally. The fix is minimal and follows the
ncurses API’s ownership rules; Linux/macOS CI should cover the affected
code path.

• Issue: Memory leak in curses module when calling initscr() after setupterm() #144067

[picnixz]

The change is incorrect as we do not know how cur_win is being used. I believe we should fix it differently but we need discussion.

Again, stop opening PRs if it has not yet been triaged. It wastes reviewer's time.

[bedevere-app]

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Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.