convert_modules.js - use empty array for Modules without Timetable
convert_modules.js - use empty array for Modules without Timetable

to simplify things when we build our Exhibit 3.0 database

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods