Don't disable pre-heat text if temperature is invalid
Don't disable pre-heat text if temperature is invalid

Otherwise you can't change the temperature to make it valid again...

Contributes to issue CURA-3161.

Curahelper/Cura,hmflash/Cura,fieldOfView/Cura,ynotstartups/Wanhao,ynotstartups/Wanhao,hmflash/Cura,fieldOfView/Cura,Curahelper/Cura