Log Message:
tqsl-2.0.2RC4 to 2.0.2RC5 change:
----------
This release fixes a pair of related defects that have been there
since TQSL 1.x

When you create a station location, you associate it with a callsign
certificate. When you sign a log, you select a location for signing,
which then uses the callsign to select the right callsign certificate.

The problems happen when you do unexpected things with those
certificates.

If you create a station location for K1MU, then delete all of the
certificates for K1MU, then signing a log would cause an "Invalid
Argument" error. TQSL has been corrected to now display an error that
there are no valid callsign certificates.

Similarly, if you create a station location and then let the
associated callsign certificate to expire, trying to sign using that
location would also give an unhelpful "Invalid Argument" message.

When there were no matching certificates, displaying the properties of
a station location would display an incorrect callsign.

These defects have been corrected in RC5 so that useful error messages
are displayed for these cases.