checker: fix break when calling unknown fn call

[felipensp]

Fix #22343

_{Huly®: V_0.6-20811}

[spytheman]

Excellent work.

By a weird coincidence, I also encountered this (or a very similar) compiler panic today, while iterating on:

fn C.puts(const_s &char) int

@[export: 'main']
fn my_main(argc int, argv &&char) int {
        C.puts(c'Hello, World!')
        return 0
}