tree-wide: avoid uninitialized warning on _cleanup_ variables

tree-wide: avoid uninitialized warning on _cleanup_ variables

With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.

(cherry picked from commit c2b2df604b845b4e1697d0911935e6644323c5a6)