Zero initialize local variables.

[kevinbackhouse]

Rebase of #1737 onto main. (Doing this manually because #1742 had some merge conflicts.)

[codecov]

Codecov Report

Merging #1743 (b235eaf) into main (fe83c73) will increase coverage by 0.00%.
The diff coverage is 73.52%.

@@           Coverage Diff           @@
##             main    #1743   +/-   ##
=======================================
  Coverage   66.89%   66.90%           
=======================================
  Files         151      151           
  Lines       20754    20786   +32     
=======================================
+ Hits        13883    13906   +23     
- Misses       6871     6880    +9     

Impacted Files	Coverage Δ
samples/Jzon.cpp	33.39% <0.00%> (-0.18%)	⬇️
src/http.cpp	0.00% <0.00%> (ø)
src/preview.cpp	57.46% <0.00%> (-0.29%)	⬇️
src/webpimage.cpp	64.97% <0.00%> (-0.17%)	⬇️
src/pgfimage.cpp	55.93% <50.00%> (-0.11%)	⬇️
src/image.cpp	72.51% <66.66%> (-0.05%)	⬇️
include/exiv2/types.hpp	90.90% <100.00%> (ø)
include/exiv2/value.hpp	90.62% <100.00%> (ø)
samples/geotag.cpp	79.36% <100.00%> (+0.27%)	⬆️
samples/largeiptc-test.cpp	79.06% <100.00%> (+1.02%)	⬆️
... and 11 more

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[hassec]

LGTM 👍

Thanks a lot @kevinbackhouse for the quick rebase :)