Multiple things wrong with `mkpwent` in `pwdmodule`

[sobolevn]

Bug report

Here's what's wrong:

• cpython/Modules/pwdmodule.c

  Lines 71 to 73 in b9cb855

  	PyObject *o = PyUnicode_DecodeFSDefault(val);
  	PyStructSequence_SET_ITEM(v, i, o);
  	}

  is not checked to be NULL, while it is possible
• All errors here can overwrite each other:

  cpython/Modules/pwdmodule.c

  Lines 88 to 104 in b9cb855

  	#define SETS(i,val) sets(v, i, val)
  	SETS(setIndex++, p->pw_name);
  	#if defined(HAVE_STRUCT_PASSWD_PW_PASSWD) && !defined(__ANDROID__)
  	SETS(setIndex++, p->pw_passwd);
  	#else
  	SETS(setIndex++, "");
  	#endif
  	PyStructSequence_SET_ITEM(v, setIndex++, _PyLong_FromUid(p->pw_uid));
  	PyStructSequence_SET_ITEM(v, setIndex++, _PyLong_FromGid(p->pw_gid));
  	#if defined(HAVE_STRUCT_PASSWD_PW_GECOS)
  	SETS(setIndex++, p->pw_gecos);
  	#else
  	SETS(setIndex++, "");
  	#endif
  	SETS(setIndex++, p->pw_dir);
  	SETS(setIndex++, p->pw_shell);

• XDECREF used, while v cannot be NULL:

  cpython/Modules/pwdmodule.c

  Line 109 in b9cb855

  Py_XDECREF(v);

I will send a PR with the fix.

Linked PRs

• gh-116545: Fix error handling in mkpwent in pwdmodule #116548
• [3.12] gh-116545: Fix error handling in mkpwent in pwdmodule (GH-116548) #116593
• [3.11] gh-116545: Fix error handling in mkpwent in pwdmodule (GH-116548) #116594