message: schat: Require explicit path to certificate.
  Don't allow using files outside of module data directory.
  This is the same requirement as for log path in log module.
diff: @@ -115,12 +115,13 @@ class CSChat : public CModule {
  ~CSChat() override {}
  bool OnLoad(const CString& sArgs, CString& sMessage) override {
  - m_sPemFile = sArgs;
  -
  - if (m_sPemFile.empty()) {
  - m_sPemFile = CZNC::Get().GetPemLocation();
  + if (sArgs.empty()) {
  + sMessage = "Argument must be path to PEM file";
  + return false;
  }
  + m_sPemFile = CDir::CheckPathPrefix(GetSavePath(), sArgs);
  +
  if (!CFile::Exists(m_sPemFile)) {
  sMessage = "Unable to load pem file [" + m_sPemFile + "]";
  return false;
  