modelcheck: capture exceptions by const reference

* tests/ltsmin/modelcheck.cc: here.

tests/ltsmin/modelcheck.cc

@@ -269,7 +269,7 @@ static int checked_main()
           model = spot::ltsmin_model::load(mc_options.model)
             .kripke(&ap, dict, deadf, mc_options.compress);
         }
-      catch (std::runtime_error& e)
+      catch (const std::runtime_error& e)
         {
           std::cerr << e.what() << '\n';
         }
@@ -322,7 +322,7 @@ static int checked_main()
             {
               res = ec->check();
             }
-          catch (std::bad_alloc&)
+          catch (const std::bad_alloc&)
           {
             std::cerr << "Out of memory during emptiness check."
                       << std::endl;
@@ -357,7 +357,7 @@ static int checked_main()
               {
                 run = res->accepting_run();
               }
-            catch (std::bad_alloc&)
+            catch (const std::bad_alloc&)
               {
                 std::cerr << "Out of memory while looking for counterexample."
                           << std::endl;
@@ -429,7 +429,7 @@ static int checked_main()
              .kripkecube(propcube->get_ap(), deadf, mc_options.compress,
                          mc_options.nb_threads);
         }
-      catch (std::runtime_error& e)
+      catch (const std::runtime_error& e)
         {
           std::cerr << e.what() << '\n';
         }
@@ -535,7 +535,7 @@ static int checked_main()
              .kripkecube({}, deadf, mc_options.compress,
                          mc_options.nb_threads);
         }
-      catch (std::runtime_error& e)
+      catch (const std::runtime_error& e)
         {
           std::cerr << e.what() << '\n';
         }
@@ -631,7 +631,7 @@ static int checked_main()
               .kripkecube({}, deadf, mc_options.compress,
                           mc_options.nb_threads);
           }
-        catch (std::runtime_error& e)
+        catch (const std::runtime_error& e)
           {
             std::cerr << e.what() << '\n';
           }