`<xlocnum>`: `num_get::do_get` for `bool` stores `true` in the result when the input has bad grouping, even if the input is zero

[cpplearner]

Describe the bug

In num_get::do_get, if _Parse_result._Bad_grouping is true, the result is set to true, regardless of the converted value of the input (_Ans).

STL/stl/inc/xlocnum

Lines 376 to 379 in 8e9f4ee

	if (_Ep == _Ac || _Errno != 0 // N4950 [facet.num.get.virtuals]/3
	|| _Parse_result._Bad_grouping) { // N4950 [facet.num.get.virtuals]/4
	_Val = true;
	_State = ios_base::failbit;

However, if I understand correctly, false should be stored when _Ans is 0 (which may happen if the input is a sequence of 0 with a misplaced thousand separator, e.g. 0,0000).

N5008 [facet.num.get.virtuals]/6, emphasis mine:

If (str.flags() & ios_base::boolalpha) == 0 then input proceeds as it would for a long
except that if a value is being stored into val, the value is determined according to the following: If
the value to be stored is 0 then false is stored. If the value is 1 then true is stored. Otherwise true
is stored and ios_base::failbit is assigned to err.

The test case below uses istream::operator>> which is defined in terms of num_get::do_get.

Command-line test case

D:\test>type test-get-bool.cpp
#include <iostream>
#include <sstream>

int main() {
    bool x;
    std::istringstream s{"0,0000"};

    std::locale loc{"en_US"};
    s.imbue(loc);

    s >> x;

    std::cout << x << '\n';
}

D:\test>cl /EHs test-get-bool.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.44.35109.1 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test-get-bool.cpp
Microsoft (R) Incremental Linker Version 14.44.35109.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test-get-bool.exe
test-get-bool.obj

D:\test>test-get-bool.exe
1

Expected behavior

test-get-bool.exe should output 0.

STL version

Microsoft Visual Studio Community 2022
Version 17.14.0 Preview 3.0