Fix crash when EAP-Message, Message-Authenticator (and User-Password) is
passed, but User-Name is not passed.

--- auth.c.orig	2010-05-07 22:44:38.966058254 +0200
+++ auth.c	2010-05-07 22:44:20.334055863 +0200
@@ -192,7 +192,7 @@
 
 	if (( auth_type_count > 1) && (debug_flag)) {
 		radlog_request(L_ERR, 0, request, "Warning:  Found %d auth-types on request for user '%s'",
-			auth_type_count, request->username->vp_strvalue);
+			auth_type_count, request->username != NULL ? request->username->vp_strvalue : "<unknown>");
 	}
 
 	/*