Fix potential encoder dead-lock after picture resize

Fix potential encoder dead-lock after picture resize

The sync interval for the multithreaded encoder was considered as not changing
during the encoding. This is not true if picture size is changed.
The encoder could dead-lock because the main thread and the other threads were
using different sync interval.

Change-Id: I75232bbdbc6c02d77f830d870fd8b4e96697c64e