Decoder: Fixed cur_mb_info initialization in error cases

When number of MBs decoded in the current frame is zero and an error is
detected, MB info was unnecessarily decremented in multi-core case.

Bug: 33351708
Bug: 33298089
Bug: 33250932
Change-Id: I150c48c6fb382736f1de855ba5384c12bf84710d
(cherry picked from commit 902c15251fe53f103f910b9f6a133e4cc7ca7416)