This change does two things:
1. It fixes the json fuzzer to account for receiving array results. Arrays are returned by the rpc server when the input data is an array.
2. Adds a `fuzz_test.go` file and corresponding `testdata` directory containing the failing test case.
This seems like a reasonable way to add and track previous crash issues in our fuzz test cases. The upcoming stdlib go fuzz tool does effectively this automatically.
