fix(richtext-lexical): order=0 being sorted to the end of the toolbar

[beheh]

What?

The following lexical editor features.BlocksFeature config:

		BlocksFeature({
			blocks: [
				BoxBlockConfig,
				MediaImageBlockConfig,
				MediaVideoBlockConfig,
				CardImageBlockConfig,
				FloatClearBlockConfig,
				EmbedBlockConfig,
			],
			// ...
		})

...currently results in a mis-sorted dropdown:

...where my custom "BoxBlockConfig" is at the end.

Why?

Because the sorting component does not consider false-y orders valid, the item with the index 0 is incorrectly sorted to the end.

How?

Switching to an explicit non-null check keeps the defensiveness while fixing this:

[beheh]

I've observed this @payloadcms/richtext-lexical@3.79.0 but have targeted main for now - not sure if you'll backport, or not, or if I should've opened against 3.X and this would've been ported to 4.X.