A stream of a kind already recorded is a guard, not a nested if

A stream of a kind already recorded is a guard, not a nested if `collapsible_match` under clippy 1.98. The match arm held nothing but an `if`, so the condition belongs in the arm: a second video stream now falls through to `_` and is ignored, which is the answer the nested form gave by doing nothing inside the arm it had already matched. Both arms take the guard, not just the one the newer clippy named — they are the same shape, and leaving one behind would mean the next release of the lint reopens this.