Mob Spawner Deletes Initial Index without Checks

Issue: when you set the initial index of a spawner to a pig and then have spawnpotentials as creeper

Steps to reproduce:
1./difficulty peaceful
2. setblock: https://pastebin.com/dVu6fDW0
3. /kill @e[type=pig]
4. /difficulty normal
5./difficulty peaceful after a good 6 seconds
6. observer never goes back to pig just spams creeper

how mojang would fix this there are multiple ways no set way but, they could do:
1. have a check each time before deleting the spawndata
2. if the new tag intialcheck is false check before deleting spawn data and if tag spawndata != spawn potentials 0 then add it to index of 0 before deleting it.
3. set the intialcheck to true