Fix Singular extension condition to handle mate scores
With Eelco's patch "Don't special case for abs(beta) >= VALUE_MATE_IN_MAX_PLY" condition "abs(ttValue) < VALUE_KNOWN_WIN" has been removed from singular extension search, and condition "abs(beta) < VALUE_KNOWN_WIN" was added to the SingularExtensionNode definition. This might lead to problems, especially in positions, where a mate is due. For example, this position 5rk1/4K1pp/8/5PPP/8/8/8/1R6 w - - 12 1 triggers an assert. stockfish: search.cpp:434: Value {anonymous}::search(Position&, Search::Stack*, Value, Value, Depth, bool) [with {anonymous}::NodeType NT = (<unnamed>::NodeType)2u; bool SpNode = false]: Assertion `-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE' failed. So let's re-insert the removed condition. First spotted by Uri Blass, fix by me. Bench: 8759675pull/13/merge
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@ -700,7 +700,8 @@ moves_loop: // When in check and at SpNode search starts from here
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&& depth >= 8 * ONE_PLY
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&& abs(beta) < VALUE_KNOWN_WIN
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&& ttMove != MOVE_NONE
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&& ttValue != VALUE_NONE
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/* && ttValue != VALUE_NONE Already implicit in the next condition */
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&& abs(ttValue) < VALUE_KNOWN_WIN
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&& !excludedMove // Recursive singular search is not allowed
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&& (tte->bound() & BOUND_LOWER)
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&& tte->depth() >= depth - 3 * ONE_PLY;
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