Fix exceptions caused when inst offering limit and/or course offering limits are null
Fix exceptions caused when inst offering limit and/or course offering limits are null

maciej-zygmunt/unitime,rafati/unitime,zuzanamullerova/unitime,maciej-zygmunt/unitime,sktoo/timetabling-system-,UniTime/unitime,maciej-zygmunt/unitime,nikeshmhr/unitime,sktoo/timetabling-system-,rafati/unitime,zuzanamullerova/unitime,sktoo/timetabling-system-,zuzanamullerova/unitime,nikeshmhr/unitime,UniTime/unitime,UniTime/unitime,nikeshmhr/unitime,rafati/unitime