Fix rays not being cast in a specific direction

A bug was introduced in 679e2b1b which caused explosions to not cast
rays for environment destruction in the (+X, +Y, +Z) direction.  This
commit fixes that.

mods/CORE/mcl_explosions/init.lua

@@ -66,50 +66,48 @@ local function compute_sphere_rays(radius)
 	local rays = {}
 	local sphere = {}
 
-	for i=1, 2 do
+	local function add_ray(pos)
+		sphere[hash_node_position(pos)] = pos
+	end
+
 	for y = -radius, radius do
 		for z = -radius, radius do
-				for x = -radius, 0, 1 do
+			for x = -radius, 0 do
 				local d = x * x + y * y + z * z
 				if d <= radius * radius then
-						local pos = { x = x, y = y, z = z }
+					add_ray(vector.new(x, y, z))
-						sphere[hash_node_position(pos)] = pos
+					add_ray(vector.new(-x, y, z))
 					break
 				end
 			end
 		end
 	end
-	end
 
-	for i=1,2 do
 	for x = -radius, radius do
 		for z = -radius, radius do
-				for y = -radius, 0, 1 do
+			for y = -radius, 0 do
 				local d = x * x + y * y + z * z
 				if d <= radius * radius then
-						local pos = { x = x, y = y, z = z }
+					add_ray(vector.new(x, y, z))
-						sphere[hash_node_position(pos)] = pos
+					add_ray(vector.new(x, -y, z))
 					break
 				end
 			end
 		end
 	end
-	end
 
-	for i=1,2 do
 	for x = -radius, radius do
 		for y = -radius, radius do
-				for z = -radius, 0, 1 do
+			for z = -radius, 0 do
 				local d = x * x + y * y + z * z
 				if d <= radius * radius then
-						local pos = { x = x, y = y, z = z }
+					add_ray(vector.new(x, y, z))
-						sphere[hash_node_position(pos)] = pos
+					add_ray(vector.new(x, y, -z))
 					break
 				end
 			end
 		end
 	end
-	end
 
 	for _, pos in pairs(sphere) do
 		rays[#rays + 1] = vector.normalize(pos)