Improve compatibility with Shredder Classic GUI

Shredder Classic GUI has a couple of issues with the UCI emitted by Stockfish, as opposed to other engines. They manifest themselves when analyzing a game move by move with multi-PV on: the eval graph goes all over the place. These 2 very simple revisions fix them.

(There is a third issue, which is IMHO a bug in the GUI, and doesn't deserve a workaround in Stockfish: when scrolling too fast through the moves, Shredder gives the engine no time to think, issuing both `go infinite` and `stop` at the same time. SF has no time to print any PV, causing the move to be displayed as 0.00)