Fix rng going out of bounds and simplify

src/openrct2-ui/windows/ProgressWindow.cpp

@@ -137,10 +137,10 @@ namespace OpenRCT2::Ui::Windows
             else
             {
                 // Pick a random style to start off with
-                std::random_device r;
-                std::uniform_int_distribution<int> uniform_dist(0, static_cast<int8_t>(std::size(kVehicleStyles)));
-                std::default_random_engine e(r());
-                style = static_cast<int8_t>(uniform_dist(e));
+                std::random_device rd;
+                std::mt19937 gen(rd());
+                std::uniform_int_distribution<int8_t> dist(0, std::size(kVehicleStyles) - 1);
+                style = dist(gen);
             }
         }