Improve UCI compliance: remove extra newline after 'bestmove' (TerjeK…

…ir#674)

Before this patch, Weiss adds an extra newline after 'bestmove'. For
example:

   $ ./weiss
 > go depth 1
 < info depth 1 seldepth 1 multipv 1 score cp 68 time 0 nodes 49 nps 49000 tbhits 0 hashfull 0 pv b1c3
 < bestmove b1c3
 <

where:
  >  input to engine
  <  output from engine

However, the additional empty line after bestmove makes python-chess
unhappy. With this simple repro:

$ python3
import chess.engine
engine = chess.engine.SimpleEngine.popen_uci('./weiss')
board = chess.Board()
result = engine.analyse(board, chess.engine.Limit(time=1)) # triggers the assert
result['score']
engine.quit()

I get:

Exception in callback Protocol._line_received('')
handle: <Handle Protocol._line_received('')>
Traceback (most recent call last):
  File "/usr/lib/python3.11/asyncio/events.py", line 80, in _run
    self._context.run(self._callback, *self._args)
  File "/home/skiminki/.local/lib/python3.11/site-packages/chess/engine.py", line 1040, in _line_received
    self.command._line_received(self, line)
  File "/home/skiminki/.local/lib/python3.11/site-packages/chess/engine.py", line 1289, in _line_received
    assert self.state in [CommandState.ACTIVE, CommandState.CANCELLING]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError
PovScore(Cp(+77), WHITE)

Technically, the UCI protocol does not list the empty output line from
the engine as an option. So, remove it to improve conformance. This also
makes the python-chess assert spam go away.

No functional change.

Bench: 19891416

src/uci.c

@@ -268,6 +268,6 @@ void PrintThinking(const Thread *thread, int alpha, int beta) {
 
 // Print conclusion of search
 void PrintConclusion(const Thread *thread) {
-    printf("bestmove %s\n\n", MoveToStr(thread->rootMoves[0].move));
+    printf("bestmove %s\n", MoveToStr(thread->rootMoves[0].move));
     fflush(stdout);
 }