we now accept empty mail addresses, when no mail address is in the vcard element
exception block has to be only around the file operations, so no wrong exception is thrown when running later in errors. added check if there is any mail address in the vcard element. if not only an empty string is used. corrected and translated some comments. uidCounter was on the wrong position.
changed a comment
mail address is now validated in the setter. an exception is now thrown when the mail address is invalid.