fix getJpegInfo to skip DHT marker

[rnigro-rwb]

Fixes #3318.

getJpegInfo now skips the DHT marker (0xc4) because that marker is not a SOF (start of frame) marker and therefore the segment to follow does not have the size information.

To add to insight to this fix, the original getJpegInfo sites http://www.64lines.com/jpeg-width-height which itself sites a reference for header info: JPEG Header Information

As you can see here, Define Huffman table marker (FFC4), 0xC4 is a marker for the Huffman table.

My fix skips 0xC4 and adjusts the remaining Start of frame (SOFn) markers to be correct.

[mbrittsess]

So, what needs to be done to get those pending checks to actually run?

[MrRio]

Let me have a look into this

[Copilot]

Pull Request Overview

This PR updates getJpegInfo to properly skip the DHT marker (0xC4) since it is not a Start Of Frame marker.

• Refines comment block to label SOF markers and note skipping of DHT
• Removes 0xc4 from the markers array
• Adjusts the list of subsequent SOF markers

Comments suppressed due to low confidence (3)

src/modules/jpeg_support.js:29

• [nitpick] Consider renaming markers to sofMarkers or SOF_MARKERS to more clearly convey that this array contains Start Of Frame markers.

  var markers = [0xc0, 0xc1, 0xc2, 0xc3, 0xc5, 0xc6, 0xc7];

src/modules/jpeg_support.js:24

• Add a unit test that includes a JPEG with a DHT segment to verify that getJpegInfo correctly skips the DHT marker and still extracts width and height.

   * 0xc4 Define Huffman Tables (DHT) - skip

src/modules/jpeg_support.js:29

• Use const instead of var for the markers array since it is not reassigned.

  var markers = [0xc0, 0xc1, 0xc2, 0xc3, 0xc5, 0xc6, 0xc7];