Disable error concealment until first key frame is decoded

When error concealment is enabled the first key frame must
be successfully received before error concealment is activated.
Error concealment will be activated when the delta following
delta frame is received.

Also fixed a couple of bugs related to error tracking in
multi-threading. And avoiding decoding corrupt residual
when we have multiple non-resilient partitions.

Change-Id: I45c4bb296e2f05f57624aef500a874faf431a60d