Use std::round() in float_to_integer_helper

[kevinbackhouse]

Fixes: #2160

std::round is double to double, so it just removes the fractional part of the number, which avoids the weird behavior of the static_cast.

[codecov]

Codecov Report

Merging #2161 (ddc96bc) into main (5d5354e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2161   +/-   ##
=======================================
  Coverage   62.65%   62.65%           
=======================================
  Files          97       97           
  Lines       19721    19721           
  Branches     9710     9710           
=======================================
  Hits        12357    12357           
  Misses       5132     5132           
  Partials     2232     2232           

Impacted Files	Coverage Δ
include/exiv2/value.hpp	84.51% <100.00%> (ø)

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[piponazo]

LGTM!

Did you also try to use the POC in 0.27-maintenance? If the error also happens there it would be good to backport the fix.

[kevinbackhouse]

@piponazo: This doesn't affect 0.27-maintenance because float_to_integer_helper is new code that I added in #2062.