[FIX] event_type: allow to select typeless event
[FIX] event_type: allow to select typeless event

The requirement for somebody to choose a ticket product should be that it is an
event, not that it has an event type attached, mostly when `event_type_id` is
not a required field.

The event has been improved in upper version but as this field is only
informative, relaxing a bit the domain.

Closes #12475

ehirt/odoo,ygol/odoo,glovebx/odoo,vnsofthe/odoo,ygol/odoo,dfang/odoo,Daniel-CA/odoo,alexcuellar/odoo,odootr/odoo,BT-ojossen/odoo,BT-ojossen/odoo,Daniel-CA/odoo,Elico-Corp/odoo_OCB,odootr/odoo,odootr/odoo,Nowheresly/odoo,tvibliani/odoo,Nowheresly/odoo,makinacorpus/odoo,NeovaHealth/odoo,OpenUpgrade/OpenUpgrade,ygol/odoo,laslabs/odoo,laslabs/odoo,bplancher/odoo,alexcuellar/odoo,tvibliani/odoo,Daniel-CA/odoo,Elico-Corp/odoo_OCB,BT-ojossen/odoo,diagramsoftware/odoo,leorochael/odoo,funkring/fdoo,Adel-Magebinary/odoo,CatsAndDogsbvba/odoo,dfang/odoo,alexcuellar/odoo,NeovaHealth/odoo,ehirt/odoo,hip-odoo/odoo,Nowheresly/odoo,dfang/odoo,ygol/odoo,Elico-Corp/odoo_OCB,synconics/odoo,makinacorpus/odoo,spadae22/odoo,datenbetrieb/odoo,synconics/odoo,ehirt/odoo,funkring/fdoo,leorochael/odoo,CatsAndDogsbvba/odoo,funkring/fdoo,funkring/fdoo,OpenUpgrade/OpenUpgrade,spadae22/odoo,CatsAndDogsbvba/odoo,alexcuellar/odoo,diagramsoftware/odoo,odootr/odoo,NeovaHealth/odoo,Adel-Magebinary/odoo,hip-odoo/odoo,glovebx/odoo,NeovaHealth/odoo,CatsAndDogsbvba/odoo,synconics/odoo,BT-ojossen/odoo,ehirt/odoo,Nowheresly/odoo,vnsofthe/odoo,spadae22/odoo,bplancher/odoo,ygol/odoo,diagramsoftware/odoo,Adel-Magebinary/odoo,leorochael/odoo,dfang/odoo,ehirt/odoo,dfang/odoo,laslabs/odoo,vnsofthe/odoo,datenbetrieb/odoo,diagramsoftware/odoo,vnsofthe/odoo,datenbetrieb/odoo,bplancher/odoo,CatsAndDogsbvba/odoo,dfang/odoo,bplancher/odoo,tvibliani/odoo,bplancher/odoo,synconics/odoo,ygol/odoo,BT-ojossen/odoo,alexcuellar/odoo,CatsAndDogsbvba/odoo,laslabs/odoo,Nowheresly/odoo,spadae22/odoo,Elico-Corp/odoo_OCB,datenbetrieb/odoo,makinacorpus/odoo,hip-odoo/odoo,Nowheresly/odoo,datenbetrieb/odoo,tvibliani/odoo,vnsofthe/odoo,alexcuellar/odoo,leorochael/odoo,spadae22/odoo,NeovaHealth/odoo,BT-ojossen/odoo,hip-odoo/odoo,glovebx/odoo,synconics/odoo,odootr/odoo,glovebx/odoo,Daniel-CA/odoo,funkring/fdoo,makinacorpus/odoo,OpenUpgrade/OpenUpgrade,spadae22/odoo,BT-ojossen/odoo,Elico-Corp/odoo_OCB,glovebx/odoo,synconics/odoo,makinacorpus/odoo,Elico-Corp/odoo_OCB,vnsofthe/odoo,OpenUpgrade/OpenUpgrade,NeovaHealth/odoo,Adel-Magebinary/odoo,bplancher/odoo,ehirt/odoo,OpenUpgrade/OpenUpgrade,laslabs/odoo,makinacorpus/odoo,hip-odoo/odoo,Daniel-CA/odoo,Nowheresly/odoo,tvibliani/odoo,diagramsoftware/odoo,vnsofthe/odoo,OpenUpgrade/OpenUpgrade,Daniel-CA/odoo,diagramsoftware/odoo,OpenUpgrade/OpenUpgrade,ehirt/odoo,ygol/odoo,leorochael/odoo,leorochael/odoo,makinacorpus/odoo,Adel-Magebinary/odoo,Adel-Magebinary/odoo,glovebx/odoo,CatsAndDogsbvba/odoo,glovebx/odoo,funkring/fdoo,alexcuellar/odoo,datenbetrieb/odoo,Adel-Magebinary/odoo,spadae22/odoo,odootr/odoo,hip-odoo/odoo,NeovaHealth/odoo,tvibliani/odoo,laslabs/odoo,Daniel-CA/odoo,diagramsoftware/odoo,leorochael/odoo,odootr/odoo,synconics/odoo,funkring/fdoo,datenbetrieb/odoo,tvibliani/odoo