PVS-Studio warning V517 for libwebpdecode

void VP8ReconstructBlock(VP8Decoder* const dec) {
  ...
  if (dec->non_zero_ & (1 << n)) {
    VP8Transform(coeffs + n * 16, dst);
  } else if (dec->non_zero_ & (1 << n)) {
    VP8TransformDC(coeffs + n * 16, dst);
  }
  ...
}

This suspicious code was found in libwebpdecode project by PVS-Studio static code analyzer.
Warning message is:
V517 The use of 'if (A) {...} else if (A) {...}' pattern was detected. There is a probability of logical error presence. Check lines: 353, 355. libwebp frame.c 353

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