Block state ids greater than 256 are converted to 256 in chunk sections that use the global palette

[garboit]

Description

If a chunk section has just switched to use the global palette and an additional block with block-state id > 256 is added, it will instead be registered as the block state with id 256 (BlockId { kind: NoteBlock, state: 6 })

Reproduction Steps

Run the following test in base/src/chunk.rs

    #[test]
    fn fill_chunk_section_with_unique_states() {
        let mut section = ChunkSection::default();

        //maximum amount of blocks before the global palette is used
        let max_block_states = (1 << MAX_BITS_PER_BLOCK) - 1;

        //place unique block states
        for i in 0..max_block_states {
            section.set_block_at(0, 0, 0, BlockId::from_vanilla_id(i + 1)).unwrap()
        }

        //the chunk section should still use a local palette.
        assert!(section.blocks.palette().is_some());

        //the next block should cause this chunk to use the global palette

        let highest_block_state = BlockId::from_vanilla_id(257);
        section.set_block_at(0,0,0, highest_block_state);
        assert_eq!(section.block_at(0, 0,0).unwrap(), highest_block_state);
    }

Output:

Left:  BlockId { kind: NoteBlock, state: 6 }
Right: BlockId { kind: NoteBlock, state: 9 }

The reason for this is that when the chunk section switches to the global palette, it still returns the old index:

feather/feather/base/src/chunk/blocks.rs

Lines 132 to 134 in 6f9e96f

	let index = p.index_or_insert(block);
	self.resize_if_needed();
	index

An easy fix would be:

let index = p.index_or_insert(block);
self.resize_if_needed();
if self.palette.is_none() {
    block.vanilla_id() as usize
} else {
    index
}

It would probably be good, if the palette returned a slice instead of an index, because then the compiler would have caught this error, but I don't have enough experience with rust to say whether this is really a better approach.