add libmagic fuzzers

libmagic library is used on untrusted files and had a history of CVEs

source: https://github.com/file/file.git
home: http://www.darwinsys.com/file/
fuzzer:

```c++
magic_t magic_open(int flags);
const char * magic_buffer(magic_t cookie, const void *buffer, size_t length);
void magic_close(magic_t cookie);
```
