Fix nextgen_bows_attach_arrows_to_entities setting

[MoNTE48]

Two minor commits. Thanks for the mod, it's cool.

[MoNTE48]

• Disable interaction with a charged bow – being close enough to a mob, the player in creative mode is more likely to kill it 1 shot simply because of the high hand damage (in some games).
  It's also pretty silly that you can interact with other nodes/entities while holding a strained bowline.

Edit. The last commit doesn't seem to be working. It's probably a Minetest Engine bug, but the hand + arrow damage is combined if the shooting player is standing close to the target. In my subgame it's 5+2 = 7. 90% chance to kill a sheep, 100% to kill a chicken with one shot and kill a cow with 2 shots.

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• Use builtin creative check:
  Starting with Minetest 5.3 a builtin feature is available and is recommended.
  minetest/minetest_game@e6aec88