Fix stale conversation list after undo.

After performing an UNDO operation, mDeferSync was not being reset to false,
which means any updates to underlying conversation cursor (such as new mail
arriving) were being ignored and not reflected in the UI.

Bug 8332559

Change-Id: Ia2e4696bc0dc15e9faee03c9dd1d2d3b1feed989
1 file changed