<syncstream>: std::osyncstream memory leak

[fsb4000]

If we change “Hello, this line is long, LEAK incoming” to be under 32 characters long, then there are no leaks detected.

Command-line test case

$ type main.cpp
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>

#include <iostream>
#include <syncstream>

int main() {
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);
    _CrtSetReportFile(_CRT_WARN, _CRTDBG_FILE_STDERR);
    _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE);
    _CrtSetReportFile(_CRT_ERROR, _CRTDBG_FILE_STDERR);
    _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE);
    _CrtSetReportFile(_CRT_ASSERT, _CRTDBG_FILE_STDERR);
    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);

    std::osyncstream bout(std::cout);
    bout << "Hello, this line is long, LEAK incoming" << '\n';
    bout.emit();
}


$ cl /std:c++20 /permissive- /EHsc /MDd /nologo main.cpp
main.cpp

$ main.exe
Hello, this line is long, LEAK incoming
Detected memory leaks!
Dumping objects ->
{205} normal block at 0x000001B70E3A0360, 32 bytes long.
 Data: <Hello, this line> 48 65 6C 6C 6F 2C 20 74 68 69 73 20 6C 69 6E 65
Object dump complete.

Expected behavior
No memory leak.

STL version

Microsoft Visual Studio Community 2022 Preview
Version 17.3.0 Preview 1.1

Additional context
This was originally reported as Devcom-10061535/VSO-1551615/AB#1551615