Correct regression in restricting a StrategySupportProfile. (#757)

This corrects the implementation of StrategySupportProfile::RestrictTo(); the previous implementation
was failing to set the (singleton) strategy list.

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Co-authored-by: Theodore Turocy <ted.turocy@gmail.com>

Author: edwardchalstrey1

src/games/stratspt.h

@@ -156,6 +156,7 @@ class StrategySupportProfile {
     const int digit = p_strategy->GetNumber() - 1;
     StrategySupportProfile restricted(*this);
     restricted.m_strategyDigits.m_allowedDigits[player_index].assign(1, digit);
+    restricted.m_support.at(player) = {p_strategy};
     return restricted;
   }
   //@}