• I agree to contribute to the project under Apache 2 License.
• 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
• The PR is proposed to the proper branch
• 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

For invalid input data there is an exception here:

which leads to missing fclose call. It's possible to wrap RGBE_ReadHeader with try-catch and call fclose in place, but I chose a more reliable way. Please let me know if another way is preferred for the fix.

The issue was found during the oss-fuzz testing.

==307898== FILE DESCRIPTORS: 1 open (0 std) at exit.
==307898== Open file descriptor 4: /tmp/__opencv_temp.R5cqbF
==307898==    at 0x4CD853B: open (open64.c:41)
==307898==    by 0x4C500B5: _IO_file_open (fileops.c:188)
==307898==    by 0x4C50411: _IO_file_fopen@@GLIBC_2.2.5 (fileops.c:280)
==307898==    by 0x4C436AD: __fopen_internal (iofopen.c:75)
==307898==    by 0x4C436AD: fopen@@GLIBC_2.2.5 (iofopen.c:86)
==307898==    by 0x662CFB: cv::HdrDecoder::readHeader() (modules/imgcodecs/src/grfmt_hdr.cpp:72)
==307898==    by 0x60315A: cv::imdecode_(cv::Mat const&, int, cv::Mat&) (modules/imgcodecs/src/loadsave.cpp:857)
==307898==    by 0x602366: cv::imdecode(cv::_InputArray const&, int) (modules/imgcodecs/src/loadsave.cpp:936)
==307898==    by 0x5F7BE2: LLVMFuzzerTestOneInput (imdecode_fuzzer.cc:51)

Test sample:
01ba0766ae85fb245abfb4e94ee828c98c772135