Runtime fix: Dirt in SPAAAAACCEEEEEEE

ndefined variable /turf/space/var/dirt
proc name: reaction turf (/datum/reagent/space_cleaner/reaction_turf)
source file: Chemistry-Reagents.dm,939
Runtime fix blood_DNA length checks when it's possibly null.

runtime error: Cannot read null.len
proc name: attack self (/obj/item/weapon/melee/telebaton/attack_self)
  source file: swords_axes_etc.dm,156
Runtime fix:  I have no UI, and I must close it.

runtime error: Cannot execute null.close().
proc name: Topic (/obj/item/device/pda/Topic)
  source file: PDA.dm,485
  usr: Garry Myers (/mob/living/carbon/human)
  src: PDA-Garry Myers (Station Engin... (/obj/item/device/pda/engineering)
  call stack:
PDA-Garry Myers (Station Engin... (/obj/item/device/pda/engineering): Topic("src=\[0x2003e95];choice=Messag...", /list (/list))
NeroHarry (/client): Topic("src=\[0x2003e95];choice=Messag...", /list (/list), PDA-Garry Myers (Station Engin... (/obj/item/device/pda/engineering))
NeroHarry (/client): Topic("src=\[0x2003e95];choice=Messag...", /list (/list), PDA-Garry Myers (Station Engin... (/obj/item/device/pda/engineering))
Runtime fix:  Someone using a gas mask with no tank...IN SPACE

runtime error: Cannot read null.oxygen
proc name: copy from (/datum/gas_mixture/proc/copy_from)
  source file: FEA_gas_mixture.dm,480
  usr: null
  src: /datum/gas_mixture (/datum/gas_mixture)
  call stack:
/datum/gas_mixture (/datum/gas_mixture): copy from(null)
Basileus (/mob/living/carbon/human): breathe()
Basileus (/mob/living/carbon/human): Life()
/datum/controller/game_control... (/datum/controller/game_controller): process mobs()
/datum/controller/game_control... (/datum/controller/game_controller): process()
runtime error: Cannot read null.toxins
proc name: breathe (/mob/living/carbon/human/proc/breathe)
  source file: life.dm,339
  usr: null
  src: Basileus (/mob/living/carbon/human)
  call stack:
Basileus (/mob/living/carbon/human): breathe()
Basileus (/mob/living/carbon/human): Life()
/datum/controller/game_control... (/datum/controller/game_controller): process mobs()
/datum/controller/game_control... (/datum/controller/game_controller): process()
Runtime fix: Alarms keep trying to heat up space.

runtime error: Cannot execute null.heat capacity().
proc name: process (/obj/machinery/alarm/process)
  source file: alarm.dm,186
runtime error: Cannot execute null.heat capacity().
proc name: process (/obj/machinery/alarm/process)
  source file: alarm.dm,186

over and over and over.
Runtime fix:  usr = 0???

runtime error: Cannot read 0.item_use_icon
proc name: remove gun icons (/client/proc/remove_gun_icons)
  source file: targeting.dm,273
  usr: 0
  src: Vivalas (/client)
  call stack:
Vivalas (/client): remove gun icons()
the taser gun (/obj/item/weapon/gun/energy/taser): dropped(Jonathon Sommer (/mob/living/carbon/human))
Jonathon Sommer (/mob/living/carbon/human): drop r hand(null)
Jonathon Sommer (/mob/living/carbon/human): update canmove()
Jonathon Sommer (/mob/living/carbon/human): Weaken(5)
Jonathon Sommer (/mob/living/carbon/human): Weaken(5)
Jonathon Sommer (/mob/living/carbon/human): apply effect(5, "weaken", 0)
Jonathon Sommer (/mob/living/carbon/human): apply effects(0, 5, 0, 0, 0, 0, 0, 0, 0)
Runtime fix:  Null isn't really that sharp.

runtime error: Cannot read null.sharp
proc name: is sharp (/proc/is_sharp)
  source file: unsorted.dm,1270
  usr: Arthur Ward (/mob/living/carbon/human)
  src: null
  call stack:
is sharp(null)
the police tape (/obj/item/tape/police): breaktape(null, Arthur Ward (/mob/living/carbon/human))
the police tape (/obj/item/tape/police): attack hand(Arthur Ward (/mob/living/carbon/human))
Arthur Ward (/mob/living/carbon/human): UnarmedAttack(the police tape (/obj/item/tape/police), 1)
Arthur Ward (/mob/living/carbon/human): ClickOn(the police tape (/obj/item/tape/police), "icon-x=16;icon-y=10;left=1;scr...")
the police tape (/obj/item/tape/police): Click(the floor (172,128,1) (/turf/simulated/floor), "mapwindow.map", "icon-x=16;icon-y=10;left=1;scr...")
Typo fix.

Screw typechecks and their need for closing parens :*(
Merge pull request #4477 from Ccomp5950/runtimefixes

Runtimefixes