corrected the check of existence previous/next event
corrected the check of existence previous/next event

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