PVS-Studio warning V557 for OpenMW

std::string rangeTypeLabel(int idx)
{
  const char* rangeTypeLabels [] = {
    "Self",
    "Touch",
    "Target"
  };
  if (idx >= 0 && idx <= 3)
    return rangeTypeLabels[idx];
  else
    return "Invalid";
}

This suspicious code was found in OpenMW project by PVS-Studio static code analyzer.
Warning message is:
V557 Array overrun is possible. The value of 'idx' index could reach 3. esmtool labels.cpp 502

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/