fix excessive measure/layout of overlays when re-rendering

When CL #I70f98f began to react to conversation overlay adapter
changes by immediately doing measure/layout, a conversation
re-render would do this O(n^2) times as it walked through the
message list cursor.

Fix this by short-circuiting measure/layout on re-render.

Change-Id: Icb9ba380555a05d87c523609af829c9a26760f74
1 file changed