gh-153862: Fix spurious color pair in curses window.inch() on a wide build

winch() returns the whole code point, so inch() replacing only its low
8 bits left the high bits in the color field.  Rebuild from
getcchar()'s attributes and color pair.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_curses.py

@@ -974,7 +974,7 @@ def test_read_from_window(self):
             with self.subTest(ch=ch):
                 stdscr.addstr(2, 0, ch)
                 self.assertEqual(stdscr.instr(2, 0, 1), b)
-                self.assertEqual(stdscr.inch(2, 0) & curses.A_CHARTEXT, b[0])
+                self.assertEqual(stdscr.inch(2, 0), b[0])
 
     def test_coordinate_errors(self):
         # Addressing a cell outside the window raises curses.error.

Modules/_cursesmodule.c

@@ -776,10 +776,10 @@ curses_getcchar(const cchar_t *wcval, wchar_t *wstr, attr_t *attrs, int *pair)
     return rtn;
 }
 
-/* winch() returns the low 8 bits of the character's code point with no locale
-   conversion, unlike instr(), so recover the locale byte from the wide cell
-   when the character maps to exactly one byte, keeping the attribute and color
-   bits in RTN.  A character with no single-byte form is left to winch(). */
+/* winch() does not convert the character to its locale byte, and its bits above
+   the character may be code-point bits rather than attributes, so rebuild the
+   value from the locale byte plus getcchar()'s attributes and color pair.  A
+   character with no single-byte form is left to winch(). */
 static chtype
 curses_cell_locale_byte(chtype rtn, const cchar_t *cell)
 {
@@ -795,7 +795,7 @@ curses_cell_locale_byte(chtype rtn, const cchar_t *cell)
        when the character has none in this locale. */
     int byte = wctob(wstr[0]);
     if (byte != EOF) {
-        rtn = (rtn & ~(chtype)A_CHARTEXT) | (unsigned char)byte;
+        rtn = (unsigned char)byte | (attrs & ~(attr_t)A_COLOR) | COLOR_PAIR(pair);
     }
     return rtn;
 }