Fix crash in autofly mod

From clean `~/.minetest` directory:
- Start waspsaliva
- Create a waypoint ".wah"
- Cheat menu -> autofly -> waypoints
- Click the new waypoint
- Click SHOW button

2021-08-19 22:24:46: ERROR[Main]: ModError: Runtime error from mod 'autoeat' in callback on_formspec_input(): *builtin*:common/vector.lua:67: attempt to index local 'pos2' (a nil value)
2021-08-19 22:24:46: ERROR[Main]: stack traceback:
2021-08-19 22:24:46: ERROR[Main]: 	*builtin*:common/vector.lua:67: in function 'direction'
2021-08-19 22:24:46: ERROR[Main]: 	*builtin*:client/wasplib.lua:503: in function 'aim'
2021-08-19 22:24:46: ERROR[Main]: 	autofly:init.lua:301: in function 'display_waypoint'
2021-08-19 22:24:46: ERROR[Main]: 	autofly:/wpforms.lua:102: in function <autofly:/wpforms.lua:77>
2021-08-19 22:24:46: ERROR[Main]: 	*builtin*:client/register.lua:26: in function <*builtin*:client/register.lua:14>
2021-08-19 22:24:46: ERROR[Main]: Check debug.txt for details.

clientmods/autofly/init.lua

@@ -296,7 +296,7 @@ function autofly.display_waypoint(name)
     local pos=name
     if type(name) ~= 'table' then pos=autofly.get_waypoint(name) end
     autofly.last_name = name
-    --autofly.last_coords = pos
+    autofly.last_coords = pos
     autofly.set_hud_info(name)
     autofly.aim(autofly.last_coords)
     autofly.display(pos,name)