Do TT cutoffs only on non pv nodes

src/search/negamax.rs

@@ -45,7 +45,8 @@ pub fn negamax(
     let entry = game.tt.lookup(game.hash);
 
     if let Some(entry) = entry {
-        if plies > 0
+        if alpha == beta - 1
+            && plies > 0
             && entry.hash == game.hash
             && entry.depth >= depth
             && entry.node_type.cutoff_eligible(entry.score, alpha, beta)