Load CSM environment after the restrictions are known

Safety-guards for CSM callbacks to abort on a bad implementation
Only run callbacks when the mods are loaded (and with it: builtin)

Duplication checks inside constructors

src/script/cpp_api/s_base.cpp

@@ -232,6 +232,13 @@ void ScriptApiBase::loadModFromMemory(const std::string &mod_name)
 void ScriptApiBase::runCallbacksRaw(int nargs,
 		RunCallbacksMode mode, const char *fxn)
 {
+#ifndef SERVER
+	// Hard fail for bad guarded callbacks
+	// Only run callbacks when the scripting enviroment is loaded
+	FATAL_ERROR_IF(m_type == ScriptingType::Client &&
+			!getClient()->modsLoaded(), fxn);
+#endif
+
 #ifdef SCRIPTAPI_LOCK_DEBUG
 	assert(m_lock_recursion_count > 0);
 #endif

src/script/cpp_api/s_security.cpp

@@ -264,6 +264,7 @@ void ScriptApiSecurity::initializeSecurityClient()
 	};
 	static const char *debug_whitelist[] = {
 		"getinfo",
+		"traceback"
 	};
 
 #if USE_LUAJIT

src/script/lua_api/l_camera.cpp

@@ -31,19 +31,24 @@ LuaCamera::LuaCamera(Camera *m) : m_camera(m)
 
 void LuaCamera::create(lua_State *L, Camera *m)
 {
+	lua_getglobal(L, "core");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	int objectstable = lua_gettop(L);
+	lua_getfield(L, -1, "camera");
+
+	// Duplication check
+	if (lua_type(L, -1) == LUA_TUSERDATA) {
+		lua_pop(L, 1);
+		return;
+	}
+
 	LuaCamera *o = new LuaCamera(m);
 	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
 	luaL_getmetatable(L, className);
 	lua_setmetatable(L, -2);
 
-	int camera_object = lua_gettop(L);
-
-	lua_getglobal(L, "core");
-	luaL_checktype(L, -1, LUA_TTABLE);
-	int coretable = lua_gettop(L);
-
-	lua_pushvalue(L, camera_object);
-	lua_setfield(L, coretable, "camera");
+	lua_pushvalue(L, lua_gettop(L));
+	lua_setfield(L, objectstable, "camera");
 }
 
 int LuaCamera::l_set_camera_mode(lua_State *L)

src/script/lua_api/l_localplayer.cpp

@@ -30,20 +30,24 @@ LuaLocalPlayer::LuaLocalPlayer(LocalPlayer *m) : m_localplayer(m)
 
 void LuaLocalPlayer::create(lua_State *L, LocalPlayer *m)
 {
+	lua_getglobal(L, "core");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	int objectstable = lua_gettop(L);
+	lua_getfield(L, -1, "localplayer");
+
+	// Duplication check
+	if (lua_type(L, -1) == LUA_TUSERDATA) {
+		lua_pop(L, 1);
+		return;
+	}
+
 	LuaLocalPlayer *o = new LuaLocalPlayer(m);
 	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
 	luaL_getmetatable(L, className);
 	lua_setmetatable(L, -2);
 
-	// Keep localplayer object stack id
-	int localplayer_object = lua_gettop(L);
-
-	lua_getglobal(L, "core");
-	luaL_checktype(L, -1, LUA_TTABLE);
-	int coretable = lua_gettop(L);
-
-	lua_pushvalue(L, localplayer_object);
-	lua_setfield(L, coretable, "localplayer");
+	lua_pushvalue(L, lua_gettop(L));
+	lua_setfield(L, objectstable, "localplayer");
 }
 
 int LuaLocalPlayer::l_get_velocity(lua_State *L)

src/script/scripting_client.cpp

@@ -84,8 +84,7 @@ void ClientScripting::InitializeModApi(lua_State *L, int top)
 
 void ClientScripting::on_client_ready(LocalPlayer *localplayer)
 {
-	lua_State *L = getStack();
-	LuaLocalPlayer::create(L, localplayer);
+	LuaLocalPlayer::create(getStack(), localplayer);
 }
 
 void ClientScripting::on_camera_ready(Camera *camera)