message: Fix crash if DXIL phi references itself
diff: @@ -1900,7 +1900,7 @@ Program::Program(const byte *bytes, size_t length)
  int64_t valSrc = LLVMBC::BitReader::svbr(op.get<uint64_t>());
  uint64_t blockSrc = op.get<uint64_t>();
  - if(valSrc < 0)
  + if(valSrc <= 0)
  {
  inst.args.push_back(Symbol(SymbolType::Unknown, m_Symbols.size() - valSrc));
  }
  