States cannot be added before StatePlugin / DefaultPlugins are added

[alice-i-cecile]

Bevy version

0.14

What you did

Added states to my app before things

What went wrong

States panicked on an unwrap.

stack backtrace:
   0: std::panicking::begin_panic_handler
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library\std\src\panicking.rs:652
   1: core::panicking::panic_fmt
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library\core\src\panicking.rs:72
   2: core::panicking::panic
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library\core\src\panicking.rs:146
   3: core::option::unwrap_failed
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library\core\src\option.rs:1984
   4: enum2$<core::option::Option<ref_mut$<bevy_ecs::schedule::schedule::Schedule> > >::unwrap
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081\library\core\src\option.rs:932
   5: bevy_state::app::impl$0::init_state<mijocraft::GameState>
             at C:\Users\pvini\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bevy_state-0.14.0-rc.4\src\app.rs:74
   6: bevy_state::app::impl$1::init_state
             at C:\Users\pvini\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bevy_state-0.14.0-rc.4\src\app.rs:186
   7: mijocraft::main
             at .\src\main.rs:32
   8: core::ops::function::FnOnce::call_once
             at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081\library\core\src\ops\function.rs:250
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Additional information

Reported on Discord. Fundamentally blocked on #69, #1255 but we can probably give a better error message.