Ryze Passive Proc Bug

Found a bug where Ryze's passive would proc without a fifth spell actually being cast.

I found this bug in a match while csing, and noticed that my passive proced, even though the spell didn't actually cast (didn't use mana, didn't do damage, didn't go on cooldown). The spell cast audio and animation started, but the target minion died before the spell landed.

Steps to Repeat:

1. Stack Ryze passive to 4.
2. As a minion is about to die, cast a targeted ability (in the video, I used E, but it's likely possible to do it with W).
3. Spell animation and audio start, but the animation does not finish, the spell does not cast, but the spell will still be counted towards stacking the Ryze's passive.

Video of the bug being repeated: https://youtu.be/IXv37xmcr6Y

Not sure if the bug is possible of being abused and having a notable impact on the game, but I would imagine that procing the shield could save someone from dying, while still allowing full use of abilities, and possibly allow them to win a fight they would have otherwise lost.