Add some safety guards to avoid empty time window use in JPetTaskIO
Add some safety guards to avoid empty time window use in JPetTaskIO

JPETTomography/j-pet-framework,alexkernphysiker/j-pet-framework,JPETTomography/j-pet-framework,alexkernphysiker/j-pet-framework,JPETTomography/j-pet-framework,alexkernphysiker/j-pet-framework,alexkernphysiker/j-pet-framework,alexkernphysiker/j-pet-framework