Fixes NE DS doorgun deployment bug (#5213)

# About the pull request
fixes #5236
fixes the issue that makes DS doorgun deploy itself into DS when placed
on NE gunslot

# Explain why it's good for the game

doorgun in wall bad


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog

:cl:
fix: bad DS doorgun placement
/:cl:

---------

Co-authored-by: Drathek <[email protected]>
Co-authored-by: harryob <[email protected]>

code/modules/cm_marines/dropship_equipment.dm

@@ -339,9 +339,10 @@
 			if(ship_base.base_category == DROPSHIP_WEAPON)
 				switch(dir)
 					if(NORTH)
-						if( istype(get_step(src, WEST), /turf/open) )
+						var/step_contents = get_step(src, EAST).contents
+						if(locate(/obj/structure) in step_contents)
 							deployed_mg.pixel_x = 5
-						else if ( istype(get_step(src, EAST), /turf/open) )
+						else
 							deployed_mg.pixel_x = -5
 					if(EAST)
 						deployed_mg.pixel_y = 9
@@ -368,12 +369,11 @@
 		if(ship_base.base_category == DROPSHIP_WEAPON)
 			switch(dir)
 				if(NORTH)
-					if( istype(get_step(src, WEST), /turf/open) )
+					var/step_contents = get_step(src, EAST).contents
+					if(locate(/obj/structure) in step_contents)
 						deployed_mg.forceMove(get_step(src, WEST))
-					else if ( istype(get_step(src, EAST), /turf/open) )
-						deployed_mg.forceMove(get_step(src, EAST))
 					else
-						deployed_mg.forceMove(get_step(src, NORTH))
+						deployed_mg.forceMove(get_step(src, EAST))
 				if(EAST)
 					deployed_mg.forceMove(get_step(src, SOUTH))
 				if(WEST)