curses.termattrs() returns a negative value on italic terminals

[fedonman]

Bug description:

curses.termattrs() returns a negative value on a terminal that advertises
A_ITALIC (bit 31), so its result cannot be passed back to the attribute
functions:

>>> curses.termattrs()
-2130771968
>>> curses.term_attrs()          # the same bits, unsigned
2164195328
>>> curses.newwin(1, 1).attrset(curses.termattrs())
OverflowError: can't convert negative value to unsigned int

This is a regression in 3.15. Up to 3.14 the macro behind it returned
PyLong_FromLong((long) X()), and on a 64-bit long the mask stayed positive.
GH-134327 rewrote it to check for ERR through an int, which sign-extends:

    int rtn = X();
    if (rtn == ERR) { ... }
    return PyLong_FromLong(rtn);

ERR checking is right for baudrate(), the macro's only other user, but
termattrs() returns a chtype mask, not a status. term_attrs(),
slk_attr() and window.getattrs() all return theirs with
PyLong_FromUnsignedLong.

CPython versions tested on:

CPython main branch, 3.14

Operating systems tested on:

Linux

Linked PRs

• gh-154874: Fix the sign of curses.termattrs() #154875
• gh-154874: Fix curses.termattrs() returning a negative attribute mask #154887