Merge pull request #27138 from vrabaud:lzw

Fix heap buffer overflow and use after free in imgcodecs #27138

This fixes:
- https://g-issues.oss-fuzz.com/issues/405243132
- https://g-issues.oss-fuzz.com/issues/405456349

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgcodecs/src/grfmt_gif.cpp

@@ -392,6 +392,8 @@ bool GifDecoder::lzwDecode() {
             if (code < colorTableSize) {
                 imgCodeStream[idx++] = (uchar)code;
             } else {
+                CV_LOG_WARNING(NULL, "Too long LZW length in GIF.");
+                CV_Assert(idx + lzwExtraTable[code].length <= width * height);
                 for (int i = 0; i < lzwExtraTable[code].length - 1; i++) {
                     imgCodeStream[idx++] = lzwExtraTable[code].prefix[i];
                 }