Add early return to solvers that apply preconditioners before first residual check

[fritzgoebel]

For the following solvers, in case of an alread good enough initial guess, we apply the preconditioner before checking the residual norm for the first time. That can be quite a bit of wasted effort, so I suggest adding a residual norm check to avoid it.

I added it for CG here, if we agree this is reasonable, it would also be applicable to

• BiCG
• FCG
• GCR

[pratikvn]

You need to update the benchmark and example outputs, but otherwise, I think this looks good.