Knockback fixes:

This PR enables knockback for snowballs, and eggs.
And disables knockback for the following mobs: Shulkers, Iron Golems,
and Ender Dragons.

mods/ENTITIES/mcl_mobs/api.lua

@@ -3210,9 +3210,10 @@ local mob_punch = function(self, hitter, tflp, tool_capabilities, dir)
 
 	local die = false
 
+
+	if damage >= 0 then
 		-- only play hit sound and show blood effects if damage is 1 or over; lower to 0.1 to ensure armor works appropriately.
 		if damage >= 0.1 then
-
 			-- weapon sounds
 			if weapon:get_definition().sounds ~= nil then
 
@@ -3238,7 +3239,7 @@ local mob_punch = function(self, hitter, tflp, tool_capabilities, dir)
 			if check_for_death(self, "hit", {type = "punch", puncher = hitter}) then
 				die = true
 			end
-
+		end
 		-- knock back effect (only on full punch)
 		if not die
 		and self.knock_back

mods/ENTITIES/mobs_mc/ender_dragon.lua

@@ -35,6 +35,7 @@ mcl_mobs:register_mob("mobs_mc:enderdragon", {
 	},
 	physical = true,
 	damage = 10,
+	knock_back = false,
 	jump = true,
 	jump_height = 14,
 	fly = true,

mods/ENTITIES/mobs_mc/iron_golem.lua

@@ -37,6 +37,7 @@ mcl_mobs:register_mob("mobs_mc:iron_golem", {
 	run_velocity = 1.2,
 	-- Approximation
 	damage = 14,
+	knock_back = false,
 	reach = 3,
 	group_attack = true,
 	attacks_monsters = true,

mods/ENTITIES/mobs_mc/shulker.lua

@@ -33,6 +33,7 @@ mcl_mobs:register_mob("mobs_mc:shulker", {
 	-- TODO: Make shulker dye-able
 	visual_size = {x=3, y=3},
 	walk_chance = 0,
+	knock_back = false,
 	jump = false,
 	drops = {
 		{name = "mcl_mobitems:shulker_shell",

mods/ITEMS/mcl_throwing/register.lua

@@ -61,11 +61,9 @@ local function check_object_hit(self, pos, dmg)
 		and entity.name ~= self.object:get_luaentity().name then
 
 			if object:is_player() and self._thrower ~= object:get_player_name() then
-				-- TODO: Deal knockback
 				self.object:remove()
 				return true
 			elseif (entity.is_mob == true or entity._hittable_by_projectile) and (self._thrower ~= object) then
-				-- FIXME: Knockback is broken
 				object:punch(self.object, 1.0, {
 					full_punch_interval = 1.0,
 					damage_groups = dmg,
@@ -185,7 +183,7 @@ local function egg_on_step(self, dtime)
 	end
 
 	-- Destroy when hitting a mob or player (no chick spawning)
-	if check_object_hit(self, pos) then
+	if check_object_hit(self, pos, 0) then
 		minetest.sound_play("mcl_throwing_egg_impact", { pos = self.object:get_pos(), max_hear_distance=10, gain=0.5 }, true)
 		self.object:remove()
 		return