Handle missing time values

[Enchufa2]

This should raise an error:

traj <- trajectory() %>%
  timeout(NA)

simmer(verbose=TRUE) %>%
  add_generator("dummy", traj, at(0)) %>%
  run() %>%
  get_mon_arrivals()
#>          0 | generator: dummy          |       new: dummy0         | 0
#>          0 |   arrival: dummy0         |  activity: Timeout        | nan
#>     name start_time end_time activity_time finished replication
#> 1 dummy0          0       NA            NA     TRUE           1

Missing time values must not reach the event queue.