Handle Unrecognized Source Indentifiers

[JeffBelgum]

Responses with unrecognized source identifiers should be handled gracefully as per the conversation in PR #10. Most likely with a "local" default.

[skrap]

Just a note that AAPL timeservers return:
[20, 1, 3, 236, 0, 0, 0, 0, 0, 0, 0, 12, 83, 72, 77, 0, 224, 182, 89, 176, 196, 179, 172, 161, 224, 182, 89, 142, 10, 0, 78, 218, 224, 182, 89, 181, 37, 251, 48, 47, 224, 182, 89, 181, 37, 252, 62, 16]
which has SHM\0 in the time field, which is causing the same issue.

[skrap]

Would you be open to a fix to this issue?