wasplib: optimize flow in ws.replace

builtin/client/wasplib.lua

@@ -772,14 +772,15 @@ end
 function ws.replace(pos,arg)
     arg=tablearg(arg)
     local nd=minetest.get_node_or_nil(pos)
-    if nd and not ws.in_list(nd.name,arg) and nd.name ~= 'air' then
+    if nd and not ws.in_list(nd.name,arg) and ws.buildable_to(pos) then
         local tm=ws.get_digtime(nd.name) or 0
         ws.dig(pos)
         minetest.after(tm + 0.1,function()
             ws.place(pos,arg)
         end)
+        return tm
     else
-        ws.place(pos,arg)
+        return ws.place(pos,arg)
     end
 end