message: fix bug where line was empty in staq compiler
diff: @@ -275,7 +275,8 @@ std::shared_ptr<IR> StaqCompiler::compile(const std::string &src,
  std::string preamble = "include \"qelib1.inc\";";
  - auto preamble_start = src.find(preamble);
  + auto preamble_start = _src.find(preamble);
  +
  // Add any required missing pre-defines that we
  // know the impl for.
  @@ -288,7 +289,8 @@ std::shared_ptr<IR> StaqCompiler::compile(const std::string &src,
  line.find("include") == std::string::npos &&
  line.find("measure") == std::string::npos &&
  line.find("qreg") == std::string::npos &&
  - line.find("creg") == std::string::npos) {
  + line.find("creg") == std::string::npos
  + && !line.empty()) {
  auto inst_name = split(line, ' ')[0];
  if (inst_name.find("(") != std::string::npos) {
  inst_name = inst_name.substr(0, inst_name.find("("));
  