Fix registration_dates_given?
Fix registration_dates_given?

When the registration period is nil registration_dates_given? should return
false.

meonkeys/osem,sonalkr132/osem,SeaGL/osem,openSUSE/osem,differentreality/osem,rishabhptr/osem,openSUSE/osem,alcho/osem,1000miles/osem,openSUSE/osem,namangupta01/osem,SeaGL/osem,differentreality/osem,ChrisBr/osem,alcho/osem,raluka/osem,AndrewKvalheim/osem,rishabhptr/osem,neilmillard/osem,AndrewKvalheim/osem,AndrewKvalheim/osem,raluka/osem,namangupta01/osem,raluka/osem,claudiug/osem,bear454/osem,Shriyanshagro/osem,differentreality/osem,kormoc/osem,bear454/osem,hennevogel/osem,1000miles/osem,ChrisBr/osem,claudiug/osem,bear454/osem,Shriyanshagro/osem,hennevogel/osem,differentreality/osem,sonalkr132/osem,SeaGL/osem,hennevogel/osem,meonkeys/osem,alcho/osem,BelieveC/osem,BelieveC/osem,kormoc/osem,1000miles/osem,Shriyanshagro/osem,rishabhptr/osem,ChrisBr/osem,neilmillard/osem,kormoc/osem,neilmillard/osem,namangupta01/osem,bear454/osem,hennevogel/osem,sonalkr132/osem,kormoc/osem,BelieveC/osem,rishabhptr/osem,raluka/osem,namangupta01/osem,Shriyanshagro/osem,claudiug/osem,BelieveC/osem,sonalkr132/osem,ChrisBr/osem,meonkeys/osem