Only mark as read voicemails with the "is_read" flag set.

The vvm sync service was querying for all voicemails with the "dirty"
bit set instead of voicemails that had actually been read and then
marking the voicemail as "read" locally. This resulted in voicemails
being marked as read that had not been listened to by the user.

Bug: 23351142
Change-Id: I24500fca0e835f643b3c635d498f51947359a481
1 file changed