include _t<n> suffix in check for existing files (#198)

* include _t<n> suffix in check for existing files

* terminate run as fast as possible if any output file exists

src/RMGRunAction.cc

@@ -239,8 +239,13 @@ std::pair<fs::path, fs::path> RMGRunAction::BuildOutputFile() const {
 
   // TODO: realpath
   auto path = fs::path(manager->GetOutputFileName());
-  if (fs::exists(path) && !manager->GetOutputOverwriteFiles()) {
-    RMGLog::Out(RMGLog::fatal, "Output file ", path.string(), " does already exists.");
+  auto path_for_overwrite =
+      fs::path(G4Analysis::GetTnFileName(path.string(), path.extension().string()));
+  if (fs::exists(path_for_overwrite) && !manager->GetOutputOverwriteFiles()) {
+    RMGLog::Out(RMGLog::error, "Output file ", path_for_overwrite.string(), " does already exists.");
+    // need to abort here (and not use ::fatal), as Geant4 is not prepared to take exceptions at
+    // this stage. also, there is no clean way to abort an run before the run started.
+    std::abort();
   }
 
   auto ext = path.extension();