Positive Y speed discarded upon exiting loaded region

After big explosions, the player can sometimes fly off with such a high speed that it will exit the loaded region before the server can load/generate new chunks. Since recent versions, a fix for dropping to the void after teleporting was added that discards the player's Y speed when not inside any chunk. However, this breaks some cannon designs.

A solution would be to only remove negative Y speeds when exiting the loaded region; This lets these vertical speed mechanics work as before without breaking the previous void fix.