[automerger] Add some error/overflow checks in codebook handling am: 6eb63e1192 am: bc4bde3bee am: 632704bab3 am: 9cea7b942e am: 57035e3928 am: 6d0e814689 am: 14cbdba347 am: c113668f32
am: efa0f5bc30

Change-Id: I8ff49c3e8e6807afe16902231dc29d2431dd5c5c