Fix glitchy y-position when colliding with a conveyor

There is this issue with conveyors where if you collide with them, your
intended next y-position doesn't get updated to the position of the
conveyor, and then your y-position gets set to your intended next
y-position. This also applies to horizontally moving platforms.

This bug used to not produce any problems, if at all, until #502 got
merged. Since then, respawning from checkpoints that are on conveyors
would sometimes not update your y-position at all, making it possible to
get stuck inside a death loop that would require you to exit the game
and re-enter it.

But you can always reliably create this bug simply by going into the
editor and placing down a conveyor and checkpoint on top of each other.
Then enter and exit playtesting a bunch of times, and you'll notice the
glitchy y-position Viridian keeps taking on.

The root cause of this is how the game moves the player whenever they
stand on the top or bottom of a conveyor (or a horizontally moving
platform). The game sets their intended next x-position (newxp), then
calls obj.entitymapcollision() on them. This would be okay, except their
intended next y-position (newyp) doesn't get set along with their newxp,
so entitymapcollision() will use the wrong newyp, then find that there
is nothing that will collide with the player at that given newyp, then
update the yp of the player to the wrong newyp.

So, the platform logic simply doesn't set the player's newyp. Why does
the player have the wrong newyp? It's because moving platforms (and
conveyors) are updated first before all other entities are, and this
includes the code that checks the player for collisions with moving
platforms. That's right: the moving platform collision code gets ran
before the player properly gets updated. This means that the game will
use the newyp of the previous frame, which could be anything, really,
but it most likely just means the intended next y-position of the player
gets canceled, leaving the player with the same y-position they had
before.

Okay, but this bug only seems to happen when you put a checkpoint inside
a conveyor (or a moving platform that hasn't started moving yet) and
start playtesting from it, so why doesn't this bug happen more often,
then? Well, it's probably because of luck and coincidence. Most of the
time, if you're colliding with a conveyor or horizontally moving
platform, you probably have a correct newyp from the previous frame of
the game, so there'd be no problems. And before #502 got merged, this
previous frame would be provided by the player having to fall to the
surface due to the y-offset of their savepoint. However, if you make it
so that you immediately teleport on to a conveyor (because you died),
then this bug will rear its ugly head.

desktop_version/src/Logic.cpp

@@ -939,6 +939,7 @@ void gamelogic()
                 if (INBOUNDS_VEC(i, obj.entities) && j > -1000)
                 {
                     obj.entities[i].newxp = obj.entities[i].xp + j;
+                    obj.entities[i].newyp = obj.entities[i].yp;
                     obj.entitymapcollision(i);
                 }
                 else
@@ -947,6 +948,7 @@ void gamelogic()
                     if (INBOUNDS_VEC(i, obj.entities) && j > -1000)
                     {
                         obj.entities[i].newxp = obj.entities[i].xp + j;
+                        obj.entities[i].newyp = obj.entities[i].yp;
                         obj.entitymapcollision(i);
                     }
                 }