[opencv] Fix core_fuzzer: catch exception by reference instead of by value

[OwenSanzas]

Summary

All catch blocks use catch (cv::Exception e) (catch by value) instead of catch (cv::Exception& e) (catch by reference). Catching by value copies the exception object, which is unnecessary and can slice derived exception types.

Fix: Change all catch (cv::Exception e) to catch (cv::Exception& e).

Coverage comparison (60 seconds, empty seed corpus, ASan, libFuzzer)

Metric	Original	Fixed	Change
Edge coverage	2536	2646	+4.34% (+110 edges)
Feature coverage	6893	7318	+6.17% (+425 features)

Note: The coverage improvement may be due to fuzzer randomness, but confirms the fix does not regress coverage.

[github-actions]

OwenSanzas has previously contributed to projects/opencv. The previous PR was #15092