PVS-Studio warning V547 for Firefox

const SafepointIndex *
IonScript::getSafepointIndex(uint32_t disp) const
{
  ....
  size_t minEntry = 0;
  ....
  size_t guess = ....;
  ....
  while (--guess >= minEntry) {
    guessDisp = table[guess].displacement();
    JS_ASSERT(guessDisp >= disp);
    if (guessDisp == disp)
      return &table[guess];
  }
  ....
}

This suspicious code was found in Firefox project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression '-- guess >= minEntry' is always true. Unsigned type value is always >= 0. ion.cpp 1112

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