allow multi-stl import also with single extruder printer

#4149

src/slic3r/GUI/Plater.cpp

@@ -2416,7 +2416,7 @@ std::vector<size_t> Plater::priv::load_files(const std::vector<fs::path>& input_
 
     auto *nozzle_dmrs = config->opt<ConfigOptionFloats>("nozzle_diameter");
 
-    bool one_by_one = input_files.size() == 1 || printer_technology == ptSLA || nozzle_dmrs->values.size() <= 1;
+    bool one_by_one = input_files.size() == 1 || printer_technology == ptSLA; // || nozzle_dmrs->values.size() <= 1; // removed by bb (toa llow multi-import on a single extruder printer.
     if (! one_by_one) {
         for (const auto &path : input_files) {
             if (std::regex_match(path.string(), pattern_bundle)) {
@@ -2729,10 +2729,11 @@ std::vector<size_t> Plater::priv::load_files(const std::vector<fs::path>& input_
 
     if (new_model != nullptr && new_model->objects.size() > 1) {
         //wxMessageDialog msg_dlg(q, _L(
-        MessageDialog msg_dlg(q, _L(
+        MessageDialog msg_dlg(q, nozzle_dmrs->values.size() > 1 ? _L(
                 "Multiple objects were loaded for a multi-material printer.\n"
                 "Instead of considering them as multiple objects, should I consider\n"
-                "these files to represent a single object having multiple parts?") + "\n",
+                "these files to represent a single object having multiple parts?") + "\n":
+                _L("Load these files as a single object with multiple parts?\n"),
                 _L("Multi-part object detected"), wxICON_WARNING | wxYES | wxNO);
         if (msg_dlg.ShowModal() == wxID_YES) {
             new_model->convert_multipart_object(nozzle_dmrs->values.size());