Fix "Received a packet for an attachment stream" error when encoding certain files.

[0xBA5E64]

I ran into an issue encoding certain mkv-files with multiple audio, subtitle and attachments, and managed to track down the issue to the way Av1an handles encoding audio; There's a lot of mapping weirdness done in ffmpeg.rs's encode_audio function:

Av1an/av1an-core/src/ffmpeg.rs

Lines 166 to 187 in 605bad6

	encode_audio.args(["-y", "-hide_banner", "-loglevel", "error", "-i"]);
	encode_audio.arg(input);
	encode_audio.args([
	"-map_metadata",
	"0",
	"-vn",
	"-dn",
	"-map",
	"0",
	"-map",
	"-0:a",
	"-c",
	"copy",
	"-map",
	"0:a",
	]);
	encode_audio.args(audio_params);
	encode_audio.arg(&audio_file);

-that ends up giving me the following error when encoding, right after Scene detection:

[matroska @ 0x560b67fa86c0] Received a packet for an attachment stream.
[aost#0:6/copy @ 0x560b67ba16c0] Error submitting a packet to the muxer: Invalid argument
[out#0/matroska @ 0x560b67b935c0] Error muxing a packet

As such, I've trimmed out many of the repeated mapping-statements to streamline the parameters. I don't know if there was a particular reason this was done the way it was before, but as far as I can tell, this works just the same way without any of the odd errors I've been encountering.

[shssoichiro]

Seems good to me, thanks