fix(renderer): handle empty array as data.blocks

[neSpecc]

Currently, if we pass [] as initial data or via blocks.render() editor will contain no-blocks at all. It will break the UX since redactorClicked will throw error:

Can not read property "holder" of undefined

editor.js/src/components/modules/ui.ts

Lines 726 to 727 in f8e9414

	const lastBlock = this.Editor.BlockManager.getBlockByIndex(-1);
	const lastBlockBottomCoord = $.offset(lastBlock.holder).bottom;

Actually .getBlockByIndex() could return undefined (if we pass an unexisting index) — so I've added undefined as the return type. But in case of getting the last block by -1 it always should return a Block since it is expected that we always have at least one Block. So I've added overload for that case instead of checking on undefined in redactorClicked

Resolves #2084

[ilyamore88]

Don't you want to publish it as a patch version?

[neSpecc]

maybe. But I don't want to include it in 2.28.0 since it has already been tested via RC.

[neSpecc]

It's not so critical since it has workaround

[MussaratAziz]

what's the workaround? @neSpecc