Swap two loops in compute_max_stats_heuristics

Profiling has shown city_tile_iterate to be expensive, with the
governors spending 20% of their time in it. They are used in a double
loop with output types. Swap the two loops to have the expensive one
outside, speeding up governors by about 15% in LTT.

common/aicore/cm.cpp

@@ -1600,18 +1600,21 @@ static void compute_max_stats_heuristic(const struct cm_state *state,
 
   output_type_iterate(stat_index)
   {
-    int base = production[stat_index];
+    pcity->citizen_base[stat_index] = production[stat_index];
+  }
 
-    city_tile_iterate(city_map_radius_sq_get(pcity), pcenter, ptile)
-    {
-      if (is_free_worked(pcity, ptile)) {
-        base += city_tile_output(pcity, ptile, is_celebrating, stat_index);
+  city_tile_iterate(city_map_radius_sq_get(pcity), pcenter, ptile)
+  {
+    if (is_free_worked(pcity, ptile)) {
+      output_type_iterate(stat_index)
+      {
+        pcity->citizen_base[stat_index] +=
+            city_tile_output(pcity, ptile, is_celebrating, stat_index);
       }
+      output_type_iterate_end;
     }
-    city_tile_iterate_end;
-    pcity->citizen_base[stat_index] = base;
   }
-  output_type_iterate_end;
+  city_tile_iterate_end;
 
   set_city_production(pcity);
   memcpy(production, pcity->prod, sizeof(pcity->prod));