Add fuzzer_metadata and fix found bugs

[ktmf01]

@rillian Could you say something about the last commit of this list, where -1 is added to an enum? It is added because this bit of API documentation says

type | The desired picture type. Use -1 to mean "any type".

But this leads to undefined behavior as -1 is not in the enum, so I added it. I'm not sure this is the best solution to the problem however, maybe you have an idea?