Add missing error message

src/potential_file_reader.cpp

@@ -42,6 +42,9 @@ PotentialFileReader::PotentialFileReader(LAMMPS *lmp,
 
   try {
     reader = open_potential(filename);
+    if(!reader) {
+      error->one(FLERR, fmt::format("cannot open {} potential file {}", potential_name, filename).c_str());
+    }
   } catch (FileReaderException & e) {
     error->one(FLERR, e.what());
   }