[BUG] `GET /channels/{channelId}/statistics` intermittently returns 500 during undeploy of an unrelated channel

[mgaffigan]

Repro:

1. In one thread, loop: deploy channel B, send a message through it, remove channel B.
2. In another thread, loop: GET /channels/{A}/statistics. GET /channels/statistics?channelId={A}&includeUndeployed=true fails the same way.

Expected:

• A request naming channel A reads only what it needs to answer about channel A.

Actual:

• Each request reads D_MS<n> for every channel the server knows about, A or not.
• Roughly one request in forty fails with HTTP 500 under the loop above.
• The server log shows
  DonkeyDaoException: java.sql.SQLSyntaxErrorException: Table/View 'D_MS<n>' does not exist,
  for the channel being removed, not for A.
• The client sees only {"message":"Request failed.","status":"500"}, because serialising the
  SQLException into the error response throws as well.