
FILE EXISTS
-----------

Checks if a file exists or not.
Everytime any of the two Filename pins is set to a NON EMPTY string, the following actions are performed:

Momentary pin not set -> both Exists Out pins are set to either True of False depending on the file existing or not;

Momentary pin set -> if the file exists, both Exists Out pins are set to True and to False suddenly after; if the file does not exist, nothing is done.
