Experimental AI: clear recruit cache when no recruit action found

(cherry-picked from commit f810504306)

data/ai/lua/generic_recruit_engine.lua

@@ -586,6 +586,9 @@ return {
 
                 return true
             else
+                -- This results in the CA being blacklisted -> clear cache
+                recruit_data.recruit = nil
+
                 return false
             end
         end