Add virtual destructor to CCoinsView

src/main.h

@@ -1825,6 +1825,9 @@ public:
 
     // Calculate statistics about the unspent transaction output set
     virtual bool GetStats(CCoinsStats &stats);
+
+    // As we use CCoinsViews polymorphically, have a virtual destructor
+    virtual ~CCoinsView() {};
 };
 
 /** CCoinsView backed by another CCoinsView */