Fix to release from block nodes. (Ladders)

fixes #1150

So here's the situation.
On block nodes, floor_pushback uses : 
if mtv_y < 0 and (not node.isPlayer or bb == node.bottom_bb) then
        node:floor_pushback(self, self.node.y - node.height)

self.node.y - node.height sets you where the bottom node collides with the block node. mvt_y smaller than 0 --> this is a locking loop if in one dt cycle you don't move up enough to leave the node. So it's either, fix how this works or enter this only when needed.
The Black magic fix only enters when when needed.
Current fix set the position so it doesn't collide. ( Better answer )