added if condition to prevent crash

scripts/krastorio2/overhaul.lua

@@ -169,7 +169,7 @@ function find_following_techs(tech, break_con)
 
     for i,v in pairs(data.raw.technology) do
         --i = techname, v = data.raw.technology[techname]
-
+        if data.raw.technology[i].prerequisites then 
             for j,w in ipairs(data.raw.technology[i].prerequisites) do
                 --prerequisites = {'el_energy_tech'}
                 --j = index, w = techname
@@ -181,6 +181,7 @@ function find_following_techs(tech, break_con)
                 end
             end
         end
+    end
 
     return return_table
 end