Block types are not checked again when decay "realizes"

[skerit]

Players on my server were reporting issues where certain blocks in their tree farms would "pop off", things like observers & pistons.
Turns out it's because the leaf decay logic queues the removal as soon as a leaf block loses contact to a log.

Once it's in this queue, it never gets checked again. Before the queue actually gets processed, a lot can happen:

• The leaf blocks could have already been removed & replaced with something else
• The leaf blocks could be connected to a log again

In my fork I just made the code check the state of the block again before actually removing it.