Fixes for the following 3 runtimes

runtime error: Cannot read null.occupant
proc name: Topic (/obj/machinery/computer/scan_consolenew/Topic)
Added a check to make sure there's an occupant.

runtime error: Cannot read null.key
proc name: toggle power (/obj/machinery/particle_accelerator/control_box/proc/toggle_power)
Added a check for if there's a usr.

runtime error: Cannot read null.backup_author
proc name: attack hand (/obj/machinery/newscaster/attack_hand)
Added a check for if the feed still exists.