Fix #620 PeopleDataGenerator::last_year bug
Fix #620 PeopleDataGenerator::last_year bug

Crash when dataset items have years outside application current bounds.

newtheatre/history-project,newtheatre/history-project,johnathan99j/history-project,johnathan99j/history-project,johnathan99j/history-project,newtheatre/history-project,newtheatre/history-project,johnathan99j/history-project,newtheatre/history-project,johnathan99j/history-project