[clang] [clang] Assertion failure on template parameter deduction failure (PR #213166)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@Sirraide @cor3ntin @mizvekov so this seems to fix the assertion being fired, but I'm super unfamiliar with template deduction land, and I've previously "fixed" template failures with completely incorrect code, hence this being a draft.

Sorry if it's so wrong I'm wasting your time :(

https://github.com/llvm/llvm-project/pull/213166