gh-123290: fix a decref usage in _cursesmodule.c

[picnixz]

Using Py_DECREF on an object that could be NULL (my bad).

• Issue: Multiple reference leaks in curses error-branches  #123290

[vstinner]

LGTM

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Android 3.x has failed when building commit 12417a9.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1594/builds/141) and take a look at the build logs.
4. Check if the failure is related to this commit (12417a9) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1594/builds/141

Failed tests:

• test_os

Failed subtests:

• test_timerfd_ns_poll - test.test_os.TimerfdTests.test_timerfd_ns_poll

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/test_os.py", line 4394, in test_timerfd_ns_poll
    self.check_timerfd_poll(True)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/test_os.py", line 4379, in check_timerfd_poll
    self.assertEqual(self.read_count_signaled(fd), 1)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 2 != 1

[mhsmith]

Buildbot failure is unrelated:

• Intermittent timerfd failure on Android #124873