Cleanup self.acc code and convert to new style vectors

mods/ENTITIES/mcl_mobs/combat.lua

@@ -830,16 +830,18 @@ local function clear_aggro(self)
 end
 
 function mob_class:do_states_attack (dtime)
-	local yaw = self.object:get_yaw() or 0
-
-	local s = self.object:get_pos()
-	local p = self.attack:get_pos() or s
-
 	self.timer = self.timer + dtime
 	if self.timer > 100 then
 		self.timer = 1
 	end
 
+	local s = self.object:get_pos()
+	if not s then return end
+
+	local p = self.attack:get_pos() or s
+
+	local yaw = self.object:get_yaw() or 0
+
 	-- stop attacking if player invisible or out of range
 	if not self.attack
 			or not self.attack:get_pos()
@@ -1141,7 +1143,13 @@ function mob_class:do_states_attack (dtime)
 			if math.random(40) == 1 then
 				self.strafe_direction = self.strafe_direction*-1
 			end
-			self.acc = vector.add(vector.multiply(vector.rotate_around_axis(vector.direction(s, p), vector.new(0,1,0), self.strafe_direction), 0.3*self.walk_velocity), stay_away_from_player)
+
+			local dir = vector.rotate_around_axis(vector.direction(s, p), vector.new(0,1,0), self.strafe_direction)
+			local dir2 = vector.multiply(dir, 0.3 * self.walk_velocity)
+
+			if dir2 and stay_away_from_player then
+				self.acc = vector.add(dir2, stay_away_from_player)
+			end
 		else
 			self:set_velocity( 0)
 		end

mods/ENTITIES/mcl_mobs/physics.lua

@@ -198,6 +198,8 @@ end
 
 -- move mob in facing direction
 function mob_class:set_velocity(v)
+	if not v then return end
+
 	local c_x, c_y = 0, 0
 
 	-- can mob be pushed, if so calculate direction
@@ -207,18 +209,15 @@ function mob_class:set_velocity(v)
 
 	-- halt mob if it has been ordered to stay
 	if self.order == "stand" or self.order == "sit" then
-	  self.acc=vector.new(0,0,0)
+		self.acc = vector.zero()
 		return
 	end
 
 	local yaw = (self.object:get_yaw() or 0) + self.rotate
 	local vv = self.object:get_velocity()
-	if vv then
-		self.acc={
-		  x = ((math.sin(yaw) * -v) + c_x)*.27,
-		  y = 0,
-		  z = ((math.cos(yaw) * v) + c_y)*.27,
-		}
+
+	if vv and yaw then
+		self.acc = vector.new(((math.sin(yaw) * -v) + c_x) * .27, 0, ((math.cos(yaw) * v) + c_y) * .27)
 	end
 end