gitweb.js: fix null object exception in initials calculation

gitweb.js: fix null object exception in initials calculation

Currently handleLine() assumes that a commit author name will always
start with a capital letter. It's possible that the author name is
user@example.com and therefore calling a match() on the name will fail
to return any matches. Subsequently joining these matches will cause an
exception. Fix by checking that we have a match before trying to join
the results into a set of initials for the author.

Signed-off-by: Stephen Boyd <redacted>
Acked-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>