ai_helper: get_unit functions should only return live units

Live beiing defined as in get_live_units(), that is, non-petrified units

(cherry-picked from commit a7d8024)

data/ai/lua/ai_helper.lua

@@ -901,12 +901,20 @@ end
 
 function ai_helper.get_units_with_moves(filter)
     -- Note: the order of the filters and the [and] tags are important for speed reasons
-    return wesnoth.get_units { { "and", { formula = "moves > 0" } }, { "and", filter } }
+    return wesnoth.get_units {
+        { "and", { formula = "moves > 0" } },
+        { "not", { status = "petrified" } },
+        { "and", filter }
+    }
 end
 
 function ai_helper.get_units_with_attacks(filter)
     -- Note: the order of the filters and the [and] tags are important for speed reasons
-    return wesnoth.get_units { { "and", { formula = "attacks_left > 0 and size(attacks) > 0" } }, { "and", filter } }
+    return wesnoth.get_units {
+        { "and", { formula = "attacks_left > 0 and size(attacks) > 0" } },
+        { "not", { status = "petrified" } },
+        { "and", filter }
+    }
 end
 
 function ai_helper.get_visible_units(viewing_side, filter)