Sqlite: Add null value

So we can distingish between a null value and zero or an empty string.

Change-Id: I9122fdafdf85cf04dcf8bca7bf294be9b28ee251
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/sqlite/sqlitebasestatement.h

@@ -74,6 +74,7 @@ public:
     int columnCount() const;
     Utils::SmallStringVector columnNames() const;
 
+    void bind(int index, NullValue);
     void bind(int index, int fetchValue);
     void bind(int index, long long fetchValue);
     void bind(int index, double fetchValue);