Why is the test flacky ? Why does this fixes it ?

In D621#11300, @deadalnix wrote:

Why is the test flacky ? Why does this fixes it ?

The first bug is in evaluation of this expression

mpool.estimateSmartFee(i, &answerFound).GetFeePerK() >origFeeEst[answerFound - 1] - deltaFee

The result incorrectly depends on prior evaluation of answerFound in LHS which is not guaranteed to happen before evaluation of RHS. (*)

The second bug is that due to the first, the use of answerFound may occur before it has even been initialized (on entry to the loop).

The fix here ensures that answerFound is properly initialized before further use (provided estimateSmartFee returns it with value > 0) , and the result of the comparison becomes determinate.

Order of evaluation of the operands of almost all C++ operators (including the order of evaluation of function arguments in a function-call expression and the order of evaluation of the subexpressions within any expression) is unspecified. The compiler can evaluate operands in any order, and may choose another order when the same expression is evaluated again.

(*) http://en.cppreference.com/w/cpp/language/eval_order

You should put the explaination in the summery of the diff.