PVS-Studio warning V579 for Firefox

void
WinUtils::LogW(const wchar_t *fmt, ...)
{
  ....
  char* utf8 = new char[len+1];
  memset(utf8, 0, sizeof(utf8));
  ....
}

Most likely this is what should be written here: memset(utf8, 0, (len+1) * sizeof(*utf8));

This suspicious code was found in Firefox project by PVS-Studio static code analyzer.
Warning message is:
V579 The memset function receives the pointer and its size as arguments. It is possibly a mistake. Inspect the third argument. winutils.cpp 146

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/