Fix uninitialized @name member in person.rb.

Fix uninitialized @name member in person.rb.

Apparently a Person can be initialized with a nil name, (presumably
from a message where there's no name given), which before this commit
resulted in the following warning:

./lib/sup/person.rb:46: warning: instance variable @name not initialized

This warning was especially unpleasant since it appeared in the current
window, causing the terminal contents to incorrectly scroll up, (as
opposed to just appearing in the log or so).