Added sanity check for every jpeg marker

[br3aker]

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Description

Discussed at #2077. Now before even trying to parse any jpeg marker decoder would check whether input stream has enough bytes available thus there's no need to check any stream.Read(...) call for return value.

Closes #2085.

[br3aker]

Note: this error message would contain hex value of the marker. While we can map byte to ITU spec name I don't think it's worth the effort.

[antonfirsov]

Changes look good. Does it make sense to construct at least one faulty image with a hex editor for regression testing? (Ideally I would overflow the last - non SOS - marker in the file.)

[br3aker]

Changes look good. Does it make sense to construct at least one faulty image with a hex editor for regression testing? (Ideally I would overflow the last - non SOS - marker in the file.)

Sounds reasonable, will create one today.

[br3aker]

@antonfirsov wow, latest release version can actually fall into really dangerous code regions for malformed jpegs.

ver2.1 stacktrace for image from linked issue:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder.JpegComponentPostProcessor.CopyBlocksToColorBuffer(Int32 spectralStep) in D:\Programming\C#\ImageSharp\src\ImageSharp\Formats\Jpeg\Components\Decoder\JpegComponentPostProcessor.cs:line 88

New stacktrace:

Unhandled exception. SixLabors.ImageSharp.InvalidImageContentException: Input stream does not have enough bytes to parse declared contents of the C4 marker.
   at SixLabors.ImageSharp.Formats.Jpeg.JpegThrowHelper.ThrowNotEnoughBytesForMarker(Byte marker) in D:\Programming\C#\ImageSharp\src\ImageSharp\Formats\Jpeg\JpegThrowHelper.cs:line 29
   at SixLabors.ImageSharp.Formats.Jpeg.JpegDecoderCore.ParseStream(BufferedReadStream stream, HuffmanScanDecoder scanDecoder, CancellationToken cancellationToken) in D:\Programming\C#\ImageSharp\src\ImageSharp\Formats\Jpeg\JpegDecoderCore.cs:line 323

[antonfirsov]

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.

Not that terrible, could be access violation 😆
Anyways, nice to have this under control, thanks!