message: Fix crash when typing a non-existent directory path
  scandir returns -1 on error.  ImGuiFileDialog was not
  checking this condition.
diff: @@ -1519,7 +1519,8 @@ namespace IGFD
  #else // dirent
  struct dirent** files = nullptr;
  size_t n = scandir(path.c_str(), &files, nullptr, inAlphaSort);
  - if (n)
  + // scandir returns -1 on error
  + if ((int)n > 0)
  {
  size_t i;
  