fix(Block): resolve HTML blocks disappearing after double setEntities

[draedful]

The cause of the bug (issue #249)

When calling setEntities({blocks:[]}) + setEntities({blocks:[b1,b2]}), the following happened in a row:

1. The first setEntities cleared the $blocksMap' → React redrawn GraphBlockwithstate = undefined→ renderednull`
2. The second setEntities created new objects BlockState → GraphBlock received BlockState_new, but getViewComponent() returned undefined (canvas component has not connected yet) → rendered null again
3. When canvas finally connected the component via setViewComponent(), React didn't know about it — ViewState was a regular variable, not a reactive one

[gravity-ui-bot]

Preview is ready.

[Antamansid]

It doesn't apply to PR, just jfyi: it doesn't check for viewstate, unlike in other places. It's probably worth adding a check on it on line 127.
like:

if (!container || !geometry || !viewState) return;