`Single` causes piped systems to panic

[MrGVSV]

Bevy version

Bevy main (ce5a82b) which is around 0.16-rc.3 tag.

What you did

I tried to run the following code:

use bevy::prelude::*;

#[derive(Component)]
struct Selected;

fn main() {
    App::new()
        .add_systems(Update, system_a.pipe(system_b))
        .run();
}

fn system_a() -> i32 {
    123
}

fn system_b(_: In<i32>, _: Single<Entity, With<Selected>>) {}

What went wrong

This code panics due to Single not matching any entities in the piped system. This behavior differs from using Single in a regular system, where it will instead just skip system execution.

Panic Message

thread 'TaskPool (6)' panicked at ~/Projects/bevy/crates/bevy_ecs/src/system/system_param.rs:445:14:
The query was expected to contain exactly one matching entity.: NoEntities("bevy_ecs::system::query::Query<bevy_ecs::entity::Entity, bevy_ecs::query::filter::With<hello_world::Selected>>")
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/panicking.rs:692:5
   1: core::panicking::panic_fmt
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:75:14
   2: core::result::unwrap_failed
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/result.rs:1704:5
   3: core::result::Result<T,E>::expect
             at ~/.rustup/toolchains/stable-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/result.rs:1061:23
   4: <bevy_ecs::system::query::Single<D,F> as bevy_ecs::system::system_param::SystemParam>::get_param
             at ./crates/bevy_ecs/src/system/system_param.rs:443:22
   5: <(P,) as bevy_ecs::system::system_param::SystemParam>::get_param
             at ./crates/bevy_ecs/src/system/system_param.rs:2144:20
   6: <bevy_ecs::system::function_system::FunctionSystem<Marker,F> as bevy_ecs::system::system::System>::run_unsafe
             at ./crates/bevy_ecs/src/system/function_system.rs:734:22
   7: <bevy_ecs::system::combinator::PipeSystem<A,B> as bevy_ecs::system::system::System>::run_unsafe
             at ./crates/bevy_ecs/src/system/combinator.rs:407:9
   8: <bevy_ecs::system::schedule_system::InfallibleSystemWrapper<S> as bevy_ecs::system::system::System>::run_unsafe
             at ./crates/bevy_ecs/src/system/schedule_system.rs:64:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Encountered a panic in system `Pipe(hello_world::system_a, hello_world::system_b)`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!

[chescock]

For some history, see #16638 (comment):

In a combination system, like a.and(b) or a.pipe(b) we're running param checks for all systems before running any of them. This results in resource_exists::<MyRes>.and(do_stuff) failing params, because do_stuff doesn't have MyRes even though it wouldn't run because of failed condition.
...
Since combination systems are incomplete, let's just ensure the first system (or the system, if no combinations are used) works correctly with fallible params, do not check params for subsequent ones and just let app crash like it did in 0.14. In 0.16 we can ship the correct param checking behavior, where we do it directly before running a system.