Use a deep copy of query stats whose values won't change during sorting.

[ChristopherSchultz]

Fixes https://bz.apache.org/bugzilla/show_bug.cgi?id=58489

[aooohan]

Another unrelated thing, it might be better to unify the coding style?
eg:

for() {
   // code
}

not:

for()
 // code

not

[ABin-Huang]

When will this problem be fixed? If necessary, I can improve and submit the code.

[ChristopherSchultz]

I reviewed this again a few months ago and, again, decided to push it off into the future.

Are you facing this particular issue? If so, it's good to have a user who can test potential fixes.

[ChristopherSchultz]

@FSchumacher How does this PR look, now?