command: fix NewCommand

[michaelkuhn]

Make an explicit copy of GlobalCommandArgs, otherwise append might overwrite it.

My recent PR for Gitea (go-gitea/gitea#5367) exposed a bug that caused wrong commands to be executed:

[...ules/context/repo.go:364 func1()] [E] GetTags: exit status 129 - error: unknown option `sort=-v:refname'
usage: git cat-file (-t [--allow-unknown-type] | -s [--allow-unknown-type] | -e | -p | <type> | --textconv | --filters) [--path=<path>] <object>

(--sort is an argument for tag, not for cat-file.)

The problem seems to be that GlobalCommandArgs is changed by append, which triggers this behavior.

[codecov-io]

Codecov Report

Merging #135 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #135      +/-   ##
==========================================
+ Coverage    32.9%   33.01%   +0.11%     
==========================================
  Files          28       28              
  Lines        1781     1784       +3     
==========================================
+ Hits          586      589       +3     
  Misses       1118     1118              
  Partials       77       77

Impacted Files	Coverage Δ
command.go	86.56% <100%> (+0.62%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6b81917...ad7491d. Read the comment docs.