Problem when adding/updating products on big catalogs

[AdrienPlx]

Hi !

I faced an issue with the module on some CLI scripts.
When the function DfCategoryBuild::buildCategory($category) is called with a non valid Category object, this line break the code and exit with an exception :

I just added a fix on the function DfCategoryBuild::build() to avoid this issue :

On the foreach, just added this code :
if (!Category::categoryExists($category)) { continue; }

Have a nice day