[MC-81497] difficulty command gets executed at the end of a tick

Relates to:

When using the difficulty command Minecraft performs it at the end of a tick.

How to reproduce:

Example command

/summon MinecartCommandBlock ~ ~1 ~ {Command:/setblock ~ ~-4 ~ redstone_block,Riding:{id:MinecartCommandBlock,Command:"",Riding:{id:MinecartCommandBlock,Command:"
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~5 ~ ~ command_block 0 replace {Command:/fill ~-1 ~ ~ ~-3 ~ ~ redstone_block}
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~4 ~ ~1 command_block 0 replace {Command:/say @e[type=PigZombie]}
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~3 ~ ~1 command_block 0 replace {Command:/summon PigZombie}
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~2 ~ ~1 command_block 0 replace {Command:/difficulty 0}
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~1 ~1 ~ stone_button 5
",Riding:{id:MinecartCommandBlock,Command:"/setblock ~1 ~ ~ command_block 0 replace {Command:/fill ~1 ~ ~ ~3 ~ ~ redstone_block}
",Riding:{id:MinecartCommandBlock,Command:"/difficulty 1
",Riding:{id:MinecartCommandBlock,Riding:{id:FallingSand,Time:1,Block:activator_rail,Riding:{id:FallingSand,Time:1,Block:redstone_block,Riding:{id:FallingSand,Time:1,Block:stone,Riding:{id:FallingSand,Time:1,Block:command_block,TileEntityData:{Command:/fill ~ ~-2 ~ ~ ~3 ~ air},Riding:{id:FallingSand,Time:1,Block:stone,Riding:{id:FallingSand,Time:1,Block:command_block,TileEntityData:{Command:/kill @e[type=MinecartCommandBlock,dy=6]}}}}}}}}}}}}}}}}}}