[llvm] [SPIR-V] Fix OpGroupAsyncCopy null event substitution (PR #212754)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> > > > Looks good to me.
> > > > If the event is not null we still generate invalid code right? Do we have a test for that?
> > > 
> > > 
> > > Yes, that's right, that is existing problem. I haven't found any tests for that, actually
> > 
> > 
> > Can you add one such that we still track that, when the event is not null, we still emit something invalid.
> 
> Yes, gonna upload as a separate PR

Here it is: https://github.com/llvm/llvm-project/pull/214222

https://github.com/llvm/llvm-project/pull/212754