coverity fixes

[neheb]

I added some builds to https://scan.coverity.com/projects/exiv2 and fixed several issues

[ghost]

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[codecov]

Codecov Report

Merging #2513 (10289f8) into main (230fbaf) will decrease coverage by 0.02%.
The diff coverage is 43.28%.

@@            Coverage Diff             @@
##             main    #2513      +/-   ##
==========================================
- Coverage   64.66%   64.65%   -0.02%     
==========================================
  Files         103      103              
  Lines       22249    22232      -17     
  Branches    10859    10858       -1     
==========================================
- Hits        14388    14373      -15     
+ Misses       5620     5618       -2     
  Partials     2241     2241              

Impacted Files	Coverage Δ
app/actions.cpp	67.91% <ø> (ø)
include/exiv2/asfvideo.hpp	66.66% <ø> (ø)
include/exiv2/image.hpp	100.00% <ø> (ø)
include/exiv2/matroskavideo.hpp	60.00% <0.00%> (+3.75%)	⬆️
include/exiv2/preview.hpp	100.00% <ø> (ø)
include/exiv2/riffvideo.hpp	100.00% <ø> (ø)
src/basicio.cpp	51.90% <ø> (ø)
src/http.cpp	0.00% <0.00%> (ø)
src/matroskavideo.cpp	4.52% <0.00%> (ø)
src/tiffcomposite_int.hpp	90.09% <ø> (-0.18%)	⬇️
... and 13 more

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