Guard malformed JPEG/TGA header fields with InvalidImageDataException

[Copilot]

ImageDecoder promises malformed inputs raise InvalidImageDataException, but two unchecked header fields could escape as IndexOutOfRangeException: progressive JPEG spectral selectors and TGA color-map entry depth. This PR adds early validation at parse boundaries so malformed files fail with the documented exception contract.

• JPEG: validate progressive scan spectral selectors

  • In ReadScan, reject invalid Ss/Se combinations before decode paths index ZigZag[64].
  • Enforced checks:
    • Ss > 63
    • Se > 63
    • Se < Ss
    • Ss == 0 && Se != 0 (spec-constrained DC-only case)

• TGA: validate color-map entry depth for mapped images

  • For colorMapType == 1, require colorMapEntryBits ∈ {8, 15, 16, 24, 32}.
  • Unsupported entry depths now throw InvalidImageDataException before palette decode/indexing.

• Regression coverage

  • Added a JPEG test mutating a progressive SOS to Ss=64, Se=64, asserting InvalidImageDataException.
  • Added a TGA test with colorMapEntryBits=0 on a color-mapped image, asserting InvalidImageDataException.

if (progressive
	&& (spectralStart > 63
	|| spectralEnd > 63
	|| spectralEnd < spectralStart
	|| (spectralStart == 0 && spectralEnd != 0)))
{
	throw new InvalidImageDataException(
		$"JPEG scan has invalid spectral selection Ss={spectralStart}, Se={spectralEnd}.");
}

• Fixes Malformed JPEG and TGA headers escape as IndexOutOfRangeException instead of InvalidImageDataException #390

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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