Function heif_have_decoder_for_format 

pub unsafe extern "C" fn heif_have_decoder_for_format(
    format: heif_compression_format,
) -> c_int

Quick check whether there is a decoder available for the given format. Note that the decoder still may not be able to decode all variants of that format. You will have to query that further (todo) or just try to decode and check the returned error.