Asking result_t for an out-of-bound src is not fatal.
Asking result_t for an out-of-bound src is not fatal.

Summary:
Similar to an earlier issue, it is possible for a result not to populate values
at a source index if they are not reachable, but it should not be an error to
request them.

Reviewed By: thezhangwei

Differential Revision: D25851296

fbshipit-source-id: 357789910d8b6187ff59529158315102e8e56a20

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex