Codechange: Replace C-style casts to size_t with static_cast. (#12455)

* Codechange: Replace C-style casts to size_t with static_cast.

This touches only simple value-type casts.

* Codechange: Replace static_cast<size_t>(-1) with SIZE_MAX

Co-authored-by: Rubidium <rubidium@openttd.org>

src/intro_gui.cpp

@@ -184,7 +184,7 @@ struct SelectGameWindow : public Window {
 
 		this->ReadIntroGameViewportCommands();
 
-		this->cur_viewport_command_index = (size_t)-1;
+		this->cur_viewport_command_index = SIZE_MAX;
 		this->cur_viewport_command_time = 0;
 		this->mouse_idle_time = 0;
 		this->mouse_idle_pos = _cursor.pos;