Sqlite: Fix null handling

Most of it is only silencing a warning but one is fixing a faulty test. So
writing null values should now be working.

Change-Id: If702e1fc8176a9e0ae82a5589c719d567929202b
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/sqlite/createtablesqlstatementbuilder.cpp

@@ -192,6 +192,8 @@ public:
             columnDefinitionString.append(defaultValue.value.toStringView());
             columnDefinitionString.append("'");
             break;
+        default:
+            break;
         }
     }