faster double and date parsing

row.h

@@ -35,6 +35,8 @@ namespace usql {
 	bool getBoolValue() override { throw Exception("getDateValue not supported on ColNullValue"); };
 
 	int compare(ColValue &other) override;
+
+	virtual ~ColNullValue() = default;
     };
 
 
@@ -52,6 +54,8 @@ namespace usql {
 	int compare(ColValue &other) override;
 
 	long m_integer;
+
+	virtual ~ColIntegerValue() = default;
     };
 
 
@@ -68,6 +72,8 @@ namespace usql {
 
 	int compare(ColValue &other) override;
 
+	virtual ~ColDoubleValue() = default;
+
 	double m_double;
     };
 
@@ -103,6 +109,8 @@ namespace usql {
 
         int compare(ColValue &other) override;
 
+	virtual ~ColDateValue() = default;
+
         long m_date;	// seconds since epoch for now
     };
 
@@ -119,6 +127,8 @@ namespace usql {
 
         int compare(ColValue &other) override;
 
+	virtual ~ColBooleanValue() = default;
+
         bool m_bool;
     };