Shooting torches with crossbow at unknown nodes crashes

[Jason Khanlar]

AsyncErr: ServerThread::run Lua: Runtime error from mod '' in callback item_OnUse(): /home/user/.minetest/mods/torch_bomb/init.lua:286: attempt to index local 'under_def' (a nil value)
stack traceback:
	/home/user/.minetest/mods/torch_bomb/init.lua:286: in function 'find_target'
	/home/user/.minetest/mods/torch_bomb/init.lua:758: in function </home/ruser/.minetest/mods/torch_bomb/init.lua:736>

When shooting torches with a crossbow at unknown nodes (boxes that have text labeled on them reading as "unknown node"), the game crashes with that message:

Steps to reproduce:

• In single player local game, use a mod that creates unique node blocks
• create unique node blocks with that mod
• exit the game, disable the mod
• start the game again, shoot a torch at the unknown node block using any of the crossbows
• crash!

[FaceDeer]

Think I fixed it, torches should now stick to unknown nodes correctly. Well, as correctly as anything that deals with unknown nodes can be.