Runtime fixes for DNA modifier, Telecomms machine unlinking, PA shutoff, and newscaster with a null wanted issue

Exact runtimes fixed: 

runtime error: Cannot read null.name
proc name: Topic (/obj/machinery/telecomms/Topic)
  source file: machine_interactions.dm,346

runtime error: Cannot read null.backup_author
proc name: attack hand (/obj/machinery/newscaster/attack_hand)
  source file: newscaster.dm,396

runtime error: Cannot read null.occupant
proc name: Topic (/obj/machinery/computer/scan_consolenew/Topic)
  source file: dna.dm,891

runtime error: Cannot read null.key
proc name: toggle power (/obj/machinery/particle_accelerator/control_box/proc/toggle_power)
  source file: particle_control.dm,211