Assert with g_synchronousClients 1

[Kazzaky]

While using current master (9c1f95c), haven't tested it on previous versions, there is error while having g_synchronousClients 1, it cause to use snapshots instead vm pps_offset, at reborn the first frame (in some cases two or more) have pm_ps->speed = 0 for some reason, which therefore cause chain reaction and set all these to "0" scale -> wishspeed -> accel and ultimately triggering assert.