Slot fallback doesn't render when using slot forwarding

[kkarpeev]

Svelte 3.31.0

Describe the bug
We have InnerComponent:

  <slot name="a">A fallback</slot>
  <slot name="b">B fallback</slot>
  <slot>Default fallback</slot>

Also we have MyComponent:

<InnerComponent>
  <slot name="a" slot="a"/>
  <slot name="b" slot="b"/>
</InnerComponent>

Then we use it like this:

<MyComponent>
  <div slot="a">Some content</div>
</MyComponent>

And in the InnerComponent we see that the fallback content of slots b and default doesn't render.
Also in the InnerComponent's script:

console.log($$slots);

// { a: true, b: true, default: true }

To Reproduce
Repl

Severity
Annoying. Blocks proper use of slot forwarding for me.

[tanhauhau]

This is fixed in 3.35.0

[kkarpeev]

Much thanks! :)

[Valexr]

but slot="b" fallback still empty...

[ash0080]

@tanhauhau
Not work, plz reopen it
#5604

https://svelte.dev/repl/ea168e49b84f46e0ba72391c1f7fb6b2?version=3.38.0