PVS-Studio warning V629 for Bitcoin

static int64_t set_vch(const std::vector<unsigned char>& vch)
{
  if (vch.empty())
    return 0;

  int64_t result = 0;
  for (size_t i = 0; i != vch.size(); ++i)
      result |= static_cast<int64_t>(vch[i]) << 8*i;

  // If the input vector's most significant byte is 0x80,
  // remove it from the result's msb and return a negative.
  if (vch.back() & 0x80)
      return -(result & ~(0x80 << (8 * (vch.size() - 1))));

   return result;
}

This suspicious code was found in Bitcoin project by PVS-Studio static code analyzer.
Warning message is:
V629 Consider inspecting the '0x80 << (8 * (vch.size() - 1))' expression. Bit shifting of the 32-bit value with a subsequent expansion to the 64-bit type. script.h 169

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