Fix previous commit which broke date parsing & palette creation

Hello,

I fixed the previous commit (a73852cb), which was maybe pushed a little bit too fast !

Two things where broken (just by opening a simple trace file):

• date parsing didn't work anymore
• a delete lead to a segfault

Philippe.

Good catch

merged

mentioned in commit bf1cd97e

Can you please have a look at these issues that have been reintroduced with this PR. Thanks https://sonarqube.bordeaux.inria.fr/sonarqube/project/issues?id=hiepacs%3Avite%3Agitlab%3Amaster&resolved=false&types=BUG