Fix payload size zero cause runtime panic on calculating padding size

[tyohan]

I got runtime panic from this line when calculating the padding size but the payload size is zero.

My code is a simple WHIP WHEP but using NACK through webrtc.NewPeerConnection(). This is happen when a browser publish a stream to WHIP endpoint and another browser trying to subscribe using WHEP.

Exception has occurred: panic
"runtime error: index out of range [-1]"
Stack:
	 3  0x0000000102a8d4d8 in github.com/pion/interceptor/pkg/nack.(*packetManager).NewPacket
	     at /Users/tyohan/go/pkg/mod/github.com/pion/[email protected]/pkg/nack/retainable_packet.go:82
	 4  0x0000000102a8c4b8 in github.com/pion/interceptor/pkg/nack.(*ResponderInterceptor).BindLocalStream.func1
	     at /Users/tyohan/go/pkg/mod/github.com/pion/[email protected]/pkg/nack/responder_interceptor.go:118
	 5  0x000000010290f3ac in github.com/pion/interceptor.RTPWriterFunc.Write
	     at /Users/tyohan/go/pkg/mod/github.com/pion/[email protected]/interceptor.go:86
	 6  0x0000000102a92d60 in github.com/pion/interceptor/pkg/report.(*SenderInterceptor).BindLocalStream.func1
	     at /Users/tyohan/go/pkg/mod/github.com/pion/[email protected]/pkg/report/sender_interceptor.go:144
	 7  0x000000010290f3ac in github.com/pion/interceptor.RTPWriterFunc.Write
	     at /Users/tyohan/go/pkg/mod/github.com/pion/[email protected]/interceptor.go:86
	 8  0x0000000102abcba0 in github.com/pion/webrtc/v4.(*interceptorToTrackLocalWriter).WriteRTP
	     at /Users/tyohan/go/pkg/mod/github.com/pion/webrtc/[email protected]/interceptor.go:147
	 9  0x0000000102afd244 in github.com/pion/webrtc/v4.(*TrackLocalStaticRTP).writeRTP
	     at /Users/tyohan/go/pkg/mod/github.com/pion/webrtc/[email protected]/track_local_static.go:172
	10  0x0000000102afd4d0 in github.com/pion/webrtc/v4.(*TrackLocalStaticRTP).Write
	     at /Users/tyohan/go/pkg/mod/github.com/pion/webrtc/[email protected]/track_local_static.go:193
	11  0x0000000102b0e3a0 in inlive.dev/live/internal/channel.NewRemoteTrack.func1
	     at /Users/tyohan/Dev/inLive/live/internal/channel/remotetrack.go:60

This PR will fix the issue

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.87%. Comparing base (bfda3e0) to head (f074cca).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/nack/retainable_packet.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #277      +/-   ##
==========================================
+ Coverage   72.81%   72.87%   +0.05%     
==========================================
  Files          79       79              
  Lines        3679     3679              
==========================================
+ Hits         2679     2681       +2     
+ Misses        866      865       -1     
+ Partials      134      133       -1     

Flag	Coverage Δ
go	72.76% <0.00%> (-0.06%)	⬇️
wasm	70.99% <0.00%> (+0.10%)	⬆️

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[Sean-Der]

Oops, thank you so much @tyohan