decoder: Reset slice header at start of slice header decode

Reset slice header to zero, to avoid using invalid slice header
contents from prior headers parsed.

Bug: 140692129
Test: poc in bug
Change-Id: Ib2b7c006069b0226b5f2d741f9da7b681be26f82
(cherry picked from commit 42f70ae4ef53a5fb663e43725000bacb5dc41d9c)
1 file changed