QWindowsPrintDevice::defaultPrintDeviceId() may crash, when no printers are installed

Analyzing a crash from a customer, we discoverd this function as the source for it:

QString QWindowsPrintDevice::defaultPrintDeviceId()
{
    DWORD size = 0;
    GetDefaultPrinter(NULL, &size);
    QScopedArrayPointer<wchar_t> name(new wchar_t[size]);
    GetDefaultPrinter(name.data(), &size);
    return QString::fromWCharArray(name.data());
}

Main requirement: No printers are installed on the windows system!

The first call of GetDefaultPrinter() will return ERROR_FILE_NOT_FOUND when no printers are installed.
size will be still zero, so the wchar_t-array allocate nothing, that means the memory name is pointing to is undefined.
The second call of GetDefaultPrinter() doesn't change anything!

The crash occures in QString::fromWCharArray(name.data());, because no buffer-size information is passed, so finally QString::fromUtf16() tries to determine the size of the buffer by finding a null-termination until size overflows after reaching MAX_INT.
Even when there is no overflow or crash, it leads to an undefined content of the QString.

The overflow depends on the state of the memory, so it is not easy to reproduce it!

Fix would be either to leave the function with a null-QString after GetDefaultPrinter() returned ERROR_FILE_NOT_FOUND or to pass the value of the DWORD size as an int to QString::fromWCharArray() to skip the length detection.

Prefered fix:

QString QWindowsPrintDevice::defaultPrintDeviceId()
{
   DWORD size = 0;
   if (!GetDefaultPrinter(NULL, &size) && size > 0)
   {
      QScopedArrayPointer<wchar_t> name(new wchar_t[size]);
      if (GetDefaultPrinter(name.data(), &size))
         return QString::fromWCharArray(name.data());
   }
   return QString();
}