Sniffers continue digging after their target block is destroyed

The Bug:

Sniffers continue digging after their target block is destroyed.

Steps to Reproduce:

1. Summon a sniffer and wait for it to begin digging.
2. Quickly break the block that the sniffer begins digging.
3. Observe the sniffer's behavior for a while.
4. Take note as to whether or not sniffers continue digging after their target block is destroyed.

Observed Behavior:

Sniffers continue digging after their target block is destroyed.

Expected Behavior:

Sniffers would stop digging after their target block is destroyed.