Fix integer overflow in print0x0007

[kevinbackhouse]

Fixes #1912.

Do the calculation in double to avoid integer overflow when the number of seconds is greater than INT_MAX.

[codecov]

Codecov Report

Merging #1913 (cd4316c) into main (774e662) will increase coverage by 0.04%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##             main    #1913      +/-   ##
==========================================
+ Coverage   60.87%   60.91%   +0.04%     
==========================================
  Files          96       96              
  Lines       19041    19047       +6     
  Branches     9726     9728       +2     
==========================================
+ Hits        11591    11603      +12     
+ Misses       5138     5132       -6     
  Partials     2312     2312              

Impacted Files	Coverage Δ
src/tags_int.cpp	76.81% <90.90%> (+0.47%)	⬆️
src/exiv2.cpp	57.85% <0.00%> (ø)
src/futils.cpp	72.06% <0.00%> (ø)
src/properties.cpp	73.36% <0.00%> (ø)
src/pentaxmn_int.cpp	72.92% <0.00%> (+0.23%)	⬆️
src/convert.cpp	53.84% <0.00%> (+0.34%)	⬆️
src/value.cpp	73.18% <0.00%> (+0.46%)	⬆️

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[kmilos]

LGTM