Fix block updates being ignored before initial build completes

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If the following sequence of events takes place:

• A chunk section is loaded and scheduled for an initial build (including creation of the world snapshot).
• A block update, etc. attempts to schedule the section for re-rendering.
• The initial build of the section completes.

it appears that the section is never actually built a second time with the new information. This causes problems with mods like AE2, which render disconnected cables initially and then connect them with a block update later. When Sodium is installed, and with a PC of the correct speed, it's possible to reliably reproduce behavior in which the cables remain visually disconnected (despite their hitbox changing) until F3+A is run manually. I was also able to make the reproduction more reliable by artificially adding a 2 second delay to chunk meshing tasks.

After several hours of tinkering and analysis, I believe I've found the culprit: the section manager explicitly avoids scheduling render updates for chunks which are not marked as built. This behavior seems incorrect; we need to process block updates as soon as the section has been added to our tracker and a snapshot of its data has been taken.

I've thus changed the logic to always schedule the block update even for non-null sections. On my system this appears to have fixed the issue, but I would like someone more familiar with the chunk tracker to validate that this does not violate some other invariant.

[embeddedt]

Nevermind, this still doesn't seem to work 100% of the time... but I do think the logic error is real.

[embeddedt]

I've created a fix that actually works and updated this to the latest dev branch. For posterity, here is the test case I made to reproduce the issue:

• Add https://modrinth.com/mod/forcecloseworldloadingscreen/version/2.1.1 to run/mods. (Needed to allow in-game GUI to display before chunks load)
• Apply this diff to the current dev branch to add ability to stall any chunk updates in progress until the U key is pressed.
• Launch the dev client and ensure always defer chunk updates is enabled.
• Create a fresh superflat world in creative mode. (It MUST be a new world, reloading an existing world causes the issue to not happen for some reason.)
• Wait for the in-game GUI to display. No chunks will be visible yet, as chunk updates are suppressed.
• Open the creative inventory, get stone, look down, and place it in front of you (I placed it two blocks away from me, not sure if that's important).
• Hold the U key until chunks start rendering.
• Observe that the stone does not render.
• Press F3+A.
• Observe that the stone now renders.

With the change in this PR, the stone renders after pressing U, without requiring an extra refresh of the chunks.