Ignore gain maps with unsupported version

[maryla-uc]

Issue #2369

[wantehchang]

LGTM. Thank you very much for working through the version checking and adding tests. It's good that you made the version check future-proof (by adding the supportedMetadataVersion variable).

Nit: The commit message could mention the change to the check of remaining data.

[leo-barnes]

@maryla-uc
I notice that supported_gainmap_writer_version_with_extra_bytes.avif is not actually a valid tmap file. The ispe property associated with the tmap has width and height set to 0.

      [ 8] ('ispe' "Image Spatial Extents", size = 20, offset = 493) {
        Version: 0, Flags: 0x000000
        Image Width: 0
        Image Height: 0
      }

[leo-barnes]

@maryla-uc I notice that supported_gainmap_writer_version_with_extra_bytes.avif is not actually a valid tmap file. The ispe property associated with the tmap has width and height set to 0.

      [ 8] ('ispe' "Image Spatial Extents", size = 20, offset = 493) {
        Version: 0, Flags: 0x000000
        Image Width: 0
        Image Height: 0
      }

Filed a new issue for it: #2391