fix #4111: replication: don't send mail when fail count is zero

fix #4111: replication: don't send mail when fail count is zero

which can happen when failing to obtain the guest's migration lock.
This led to a lot of mails being sent during migration (timeout for
obtaining lock is only 2 seconds and we run it in a loop).

One could argue that obtaining the lock should increase the fail
count, but without the lock, the job state should not be touched and
even the first three mails upon migration could be considered spam.

Fixes: fa4bb659 ("replication: sent always mail for first three tries and move helper")
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>