Digital Miner additional Fixes

This is a slight change to the digital miner search thread to remove the
object creation that occurs for each block checked. It is a sort of
minor thing, but it will help to keep the memory requirements for the
thread down and execution maybe slightly faster.

Edit 1: Added a fix for the digital miner freezing when not encountering a block that it expects.
Edit 2: Added commit to remove blocks in unloaded chunks from consideration while mining.