[analyzer] Fix dead store checker false positive

It is common to zero-initialize not only scalar variables,
but also structs.  This is also defensive programming and
we shouldn't complain about that.

rdar://34122265

Differential Revision: https://reviews.llvm.org/D99262

GitOrigin-RevId: 9f0d8bac144c8eb1ca4aff823b2e2d5a0f990072
2 files changed