message: add filepath check for importers
diff: #include "app/ospStudio.h"
  +#include <sys/stat.h>
  +
  namespace ospray {
  namespace sg {
  @@ -136,6 +138,12 @@ struct OSPSG_INTERFACE Importer : public Node
  extern OSPSG_INTERFACE AssetsCatalogue cat;
  extern OSPSG_INTERFACE std::map<std::string, std::string> importerMap;
  +inline bool checkFilepath(const char *file)
  +{
  + struct stat buffer;
  + return stat(file, &buffer) == 0 && (buffer.st_mode & S_IFDIR) == 0;
  +}
  +
  // Providing a unique transform instance as root to add existing imported model to,
  // should probably be the responsibility of the calling routine
  inline std::shared_ptr<Importer> getImporter(
  @@ -152,6 +160,13 @@ inline std::shared_ptr<Importer> getImporter(
  free(cTemp);
  std::string baseName = fileName.name();
  +
  + if (!checkFilepath(fileName.c_str())) {
  + std::cerr << "#osp:sg: Filepath does not exist for '" << fileName.base()
  + << "'" << std::endl;
  + return nullptr;
  + }
  +
  auto fnd = importerMap.find(rkcommon::utility::lowerCase(fileName.ext()));
  if (fnd == importerMap.end()) {
  std::cout << "No importer for " << fileName << std::endl;
  