Fix thistle not getting dug by water properly

mods/default/functions.lua

@@ -131,11 +131,14 @@ minetest.register_lbm(
 -- Vertical plants
 
 function default.dig_up(pos, node, digger)
-   --	if digger == nil then return end
    local np = {x = pos.x, y = pos.y + 1, z = pos.z}
    local nn = minetest.get_node(np)
    if nn.name == node.name then
-      minetest.node_dig(np, nn, digger)
+      if digger then
+         minetest.node_dig(np, nn, digger)
+      else
+         minetest.remove_node(np)
+      end
    end
 end
 

mods/default/nodes.lua

@@ -1067,6 +1067,9 @@ minetest.register_node(
       after_dig_node = function(pos, node, metadata, digger)
          default.dig_up(pos, node, digger)
       end,
+      on_flood = function(pos, oldnode, newnode)
+         default.dig_up(pos, oldnode)
+      end,
 })
 
 -- Food