check for malformed table in scan_for_tube_objects()

diff --git a/autoplace_tubes.lua b/autoplace_tubes.lua
index 385458c7de94a934b5e5cf698dee8ebddec1caf5..c9d5d9f688c0e849c7834810954ecf7cd5fb22e5 100644 (file)
--- a/autoplace_tubes.lua
+++ b/autoplace_tubes.lua
@@ -131,7 +131,7 @@ local function tube_autoroute(pos)
 end
 
 function pipeworks.scan_for_tube_objects(pos)
-       if pos == nil then return end
+       if not pos or not pos.x or not pos.y or not pos.z then return end
        tube_autoroute({ x=pos.x-1, y=pos.y  , z=pos.z   })
        tube_autoroute({ x=pos.x+1, y=pos.y  , z=pos.z   })
        tube_autoroute({ x=pos.x  , y=pos.y-1, z=pos.z   })