Nested transitions prevent items from being removed

[Rich-Harris]

Looks like there is some stale state somewhere, and Svelte thinks items are in the process of being removed (or something) https://svelte.technology/repl?version=2.9.7&gist=1b5b2cc92dfb9af877487c464739df0f

[jacwright]

Looks like the each_blocks array size isn't being adjusted. Will work on it.