Fixes an exoplanet runtime. (#18372)

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/overmap/exoplanets/exoplanet.dm

@@ -226,7 +226,7 @@
 			if(istype(T) && T.zone && T.zone.contents.len > (maxx*maxy*0.25)) //if it's a zone quarter of zlevel, good enough odds it's planetary main one
 				Z = T.zone
 				break
-		if(Z && !Z.fire_tiles.len && !atmosphere.compare(Z.air)) //let fire die out first if there is one
+		if(Z && !length(Z.fire_tiles) && !atmosphere.compare(Z.air)) //let fire die out first if there is one
 			var/datum/gas_mixture/daddy = new() //make a fake 'planet' zone gas
 			daddy.copy_from(atmosphere)
 			daddy.group_multiplier = Z.air.group_multiplier

html/changelogs/mattatlas-exort.yml

@@ -0,0 +1,41 @@
+################################
+# Example Changelog File
+#
+# Note: This file, and files beginning with ".", and files that don't end in ".yml" will not be read. If you change this file, you will look really dumb.
+#
+# Your changelog will be merged with a master changelog. (New stuff added only, and only on the date entry for the day it was merged.)
+# When it is, any changes listed below will disappear.
+#
+# Valid Prefixes:
+#   bugfix
+#   wip (For works in progress)
+#   tweak
+#   soundadd
+#   sounddel
+#   rscadd (general adding of nice things)
+#   rscdel (general deleting of nice things)
+#   imageadd
+#   imagedel
+#   maptweak
+#   spellcheck (typo fixes)
+#   experiment
+#   balance
+#   admin
+#   backend
+#   security
+#   refactor
+#################################
+
+# Your name.
+author: MattAtlas
+
+# Optional: Remove this file after generating master changelog.  Useful for PR changelogs that won't get used again.
+delete-after: True
+
+# Any changes you've made.  See valid prefix list above.
+# INDENT WITH TWO SPACES.  NOT TABS.  SPACES.
+# SCREW THIS UP AND IT WON'T WORK.
+# Also, all entries are changed into a single [] after a master changelog generation. Just remove the brackets when you add new entries.
+# Please surround your changes in  double quotes ("), as certain characters otherwise screws up compiling. The quotes will not show up in the changelog.
+changes:
+  - bugfix: "Fixed an exoplanet processing error."