Don't filter root moves if MultiPV mode is enabled

A band-aid patch to workaround current TB code
limitations with multi PV.

Hopefully this will be removed after committing the
big update of TB impementation, now under discussion.

No functional change.

src/search.cpp

@@ -1588,6 +1588,10 @@ void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves)
     ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
     Cardinality = Options["SyzygyProbeLimit"];
 
+    // Don't filter any moves if the user requested analysis on multiple
+    if (Options["MultiPV"] != 1)
+        return;
+
     // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
     if (Cardinality > MaxCardinality)
     {