bugfix(compat): Improve WideCharToMultiByte reliability and query mode

Dependencies/Utility/Utility/wchar_compat.h

@@ -30,5 +30,27 @@ typedef WCHAR* LPWSTR;
 // MultiByteToWideChar
 #define CP_ACP 0
 #define MultiByteToWideChar(cp, flags, mbstr, cb, wcstr, cch) mbstowcs(wcstr, mbstr, cch)
-#define WideCharToMultiByte(cp, flags, wcstr, cch, mbstr, cb, defchar, used) wcstombs(mbstr, wcstr, cb)
+
+// WideCharToMultiByte replacement:
+// The real Windows API supports a "query mode" where mbstr==nullptr and cb==0, which returns
+// the required buffer size. wcstombs(nullptr, wcstr, 0) is unreliable on some CRT
+// implementations (e.g. Windows CRT via MinGW), so we use an inline function instead.
+inline int WideCharToMultiByte(unsigned int /*cp*/, unsigned long /*flags*/,
+                               const wchar_t* wcstr, int /*cch*/,
+                               char* mbstr, int cb,
+                               const char* /*defchar*/, int* /*used*/)
+{
+    if (!wcstr)
+        return 0;
+    if (!mbstr || cb == 0)
+    {
+        // Query mode: return the required buffer size (number of bytes including null terminator)
+        size_t len = wcslen(wcstr);
+        return static_cast<int>(len + 1);
+    }
+    size_t converted = wcstombs(mbstr, wcstr, static_cast<size_t>(cb));
+    if (converted == static_cast<size_t>(-1))
+        return 0;
+    return static_cast<int>(converted);
+}