GET /project/.../purchase_lists fails with 500 if purchase list has no date

[Daniel Böhmer]

• either enforce date
• or fix controller/template code

[error] DBIx::Class::InflateColumn::DateTime::catch {...} (): Error while inflating '' for date on Coocook::Model::DB::PurchaseList=HASH(0x564d25eb5de0): Invalid date format:  at /home/coocook/perl5/perlbrew/perls/perl-5.30.1/lib/site_perl/5.30.1/Catalyst/Action.pm line 358. at /home/coocook/coocook/lib/Coocook/Controller/Print.pm line 62