Fix crash in InspectorWindow.

- In the case where retrieval of a memory block failed, InspectorWindow
didn't handle the notification. Consequently, it never removed itself as
a listener from the failed block, nor did it release its reference for
it. Consequently, if one attempted to retrieve data from the same block
again, walking the listener list would crash due to the already-deleted
entry in the list.

- The success case had the same problem with regards to not removing its
listener, but was masked by virtue of the inspector currently being the
only user of the memory block manager, so in the latter case the blocks
would be properly released/destroyed and the aforementioned walk would
never occur.

- Adjust locking a bit to ensure that manipulating the listener list
always happens with the team lock held.

- Style fixes.
InspectorWindow: slight behaviorial tweak in failure case.

Don't release the reference to the current block until we get the
notification that the next block has been retrieved. Otherwise, the
previous/next block buttons would cease to work if the requested block
failed to be retrieved.