Fix ICE in `loops` module
changelog: Fix ICE related to `needless_collect` when a call to `iter()` was not present.
I went for restoring the old suggestion of `next().is_some()` over `get(0).is_some()` given that `iter()` is not necessarily present (could be e.g. `into_iter()` or `iter_mut()`) and that the old suggestion could change semantics, e.g. a call to `filter()` could be present between `iter()` and the collect part.
Fixes#5872
70c46de012