Code review comment for lp:~dandrader/mir/switchingBundle_lp1270964

This solution is indeed technically correct. Although I would personally take a simpler approach and initialize last_consumed to 0xdeadbeef or something similar. Then the caller has much less (1 in 4 billion) chance of accidentally writing code than could trigger the bug. And no need for a new member.

Fortunately I just realized and remembered Mir presently has 0% chance of experiencing the bug. Because our real compositor starts at frame #1.