fix: load LuaSocket/socket.lua from base VFS in LuaMenu (fixes lobby networking)

CLuaMenu::InitLuaSocket looked for 'socket.lua' in the default VFS, which
never resolved, so the menu/lobby's LuaSocket never initialised and Chobby
logged 'Error loading socket.lua' and could not connect to multiplayer
servers. socket.lua actually ships in springcontent.sdz at
LuaSocket/socket.lua; load it from SPRING_VFS_BASE with a FileExists guard,
matching CLuaUI::InitLuaSocket.

Author: Mearman

rts/Lua/LuaMenu.cpp

@@ -137,8 +137,18 @@ string CLuaMenu::LoadFile(const string& name) const
 void CLuaMenu::InitLuaSocket(lua_State* L) {
 	RECOIL_DETAILED_TRACY_ZONE;
 	std::string code;
-	std::string filename = "socket.lua";
-	CFileHandler f(filename);
+	// socket.lua ships in springcontent.sdz under LuaSocket/; load it from
+	// the base VFS exactly as CLuaUI::InitLuaSocket does. The previous path
+	// ("socket.lua", default VFS) never resolved, so the menu/lobby's
+	// LuaSocket support failed to initialise ("Error loading socket.lua"),
+	// breaking multiplayer server connections from Chobby.
+	std::string filename = "LuaSocket/socket.lua";
+	CFileHandler f(filename, SPRING_VFS_BASE);
+
+	if (!f.FileExists()) {
+		LOG_L(L_ERROR, "Error loading %s (file does not exist)", filename.c_str());
+		return;
+	}
 
 	LUA_OPEN_LIB(L, luaopen_socket_core);