Decouple EXIV2_BUILD_FUZZ_TESTS from EXIV2_TEAM_USE_SANITIZERS.

[kevinbackhouse]

The build is failing on OSS-Fuzz because their script wants to control the sanitizer flags like -fsanitize=address itself. So I think we need to separate EXIV2_BUILD_FUZZ_TESTS from EXIV2_TEAM_USE_SANITIZERS. The first only adds -fsanitize=fuzzer-no-link and the second adds -fsanitize=address,undefined.

I have also fixed a few of those annoying UBSAN failures caused by memcpy with a NULL pointer (and a zero size argument).

[codecov]

Codecov Report

Merging #1869 (2d248ad) into main (dcb65d9) will decrease coverage by 0.00%.
The diff coverage is 66.66%.

❗ Current head 2d248ad differs from pull request most recent head 64fe776. Consider uploading reports for the commit 64fe776 to get more accurate results

@@            Coverage Diff             @@
##             main    #1869      +/-   ##
==========================================
- Coverage   60.78%   60.77%   -0.01%     
==========================================
  Files          96       96              
  Lines       18881    18887       +6     
  Branches     9494     9498       +4     
==========================================
+ Hits        11476    11478       +2     
- Misses       5115     5116       +1     
- Partials     2290     2293       +3     

Impacted Files	Coverage Δ
src/pngimage.cpp	59.84% <50.00%> (-0.22%)	⬇️
src/jpgimage.cpp	70.05% <66.66%> (-0.10%)	⬇️
src/tiffvisitor_int.cpp	75.75% <66.66%> (-0.09%)	⬇️
src/basicio.cpp	48.76% <100.00%> (+0.06%)	⬆️

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[clanmills]

Guys. Can you update README.md concerning this, please. The behaviour of $ make tests has changed considerably on 'main' and README.md should also be updated to deal with that.

I made small changes to README.md on 0.27-maintenance yesterday. I fixed a couple of typos and clarified using gtest 1.8.0. Something weird occurred on GitHub yesterday afternoon and those changes didn't get into RC1. I'll fix that shortly.

If you're updating README.md, please use version in #1865. Better to wait for me to fix it in 0.27-maintenance.

[clanmills]

Right. I've fixed README.md on 0.27-maintenance. #1870.

When README.md is updated to branch main to explain the behaviour of $ make test on v1.00, you'll probably also have to update README-CONAN.md appropriately.