PVS-Studio warning V607 for TPP

Boolean MixtureModel::iterate(int counter) {
  ....
  if (done_[charge] < 0) {
    done_[charge];
  }
  else if (priors_[charge] > 0.0) {
    done_[charge] += extraitrs_;
  }
  ....
}

This suspicious code was found in TPP project by PVS-Studio static code analyzer.
Warning message is:
V607 Ownerless expression 'done_[charge]'. mixturemodel.cxx 1558

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