[contrib] validate_failures.py: Another fix for GCC's results

Some of GCC's random .json results files cannot even be parsed.
(for instance gotools/check-go-dir/src/cmd/internal/test2json/testdata/ascii.json)

Skip them intead of crashing.

Change-Id: Ib8b0ecfffeef932a3114181c351d3460c558b52a
1 file changed