Add check before inserting values in the LWWMap

When adding an integer/double value in the LWWMap, if the input value field is blank or if it doesn't contain a number, it will add an empty string '' in the map. And it will generate an error when we will use the iterator to render the LWWMap.

The root of the problem: c-crdtlib#103

added bug::major label

created merge request !12 (merged) to address this issue

mentioned in merge request !12 (merged)

added Workflow::Ready for review label

closed with merge request !12 (merged)

mentioned in commit 7356d923

removed Workflow::Ready for review label