lib: Use email address instead of empty real name.

lib: Use email address instead of empty real name.

Currently, if a From-header is of the form:

    "" <address@example.com>

the empty string will be treated as a valid real-name, and the entry
in the search results will be empty.

The new behavior here is that we treat an empty real-name field as if
it were null, so that the email address will be used in the search
results instead.

Signed-off-by: Jesse Rosenthal <jrosenthal@jhu.edu>