Cactus: CCTK_ParameterWalk: Avoid uninitialized variable
Issue #2702 resolved
Ensure `next_index` is re-initialized every time.
Otherwise there is a code path where
CCTK_ParameterWalk is called with
next_index is not reset to
0 before it is used.
Applied as git hash 6f3d8ad4 "Merged in eschnett/parameters-init (pull request
#150)" of cactus