fix(delagent): repair generation of hash for authentication

• The function SHA1(...) could generate strings containing \000 which did not work with the following call of strlen(...)
• This is solved, since one knows that a SHA1 hash as hex is 40 characters long (20 chars for the raw value)
• The old test, whether the creation of the sha1 failed, can not work since the first char could also be \000 ==> removed