[KillDeathBusiness] 修正値が前処理で負数になっても動くように

[ysakasin]

判定コマンドJDでJD5+(1-2),4のように負数が前処理で展開されると動かない問題を修正。

Fix #272

[codecov]

Codecov Report

Merging #346 (0bb7763) into master (e4c4fe1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #346   +/-   ##
=======================================
  Coverage   94.43%   94.43%           
=======================================
  Files         263      263           
  Lines       18049    18055    +6     
=======================================
+ Hits        17044    17050    +6     
  Misses       1005     1005           

Impacted Files	Coverage Δ
lib/bcdice/game_system/KillDeathBusiness.rb	96.61% <100.00%> (+0.11%)	⬆️

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