fix segfault?

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@3114 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/endpoints/mod_sofia/mod_sofia.c

@@ -855,6 +855,10 @@ char *encode_name(char *s)
 	char *at, *resource;
 	char *user;
 
+	if (!s) {
+		return NULL;
+	}
+
 	if (!strchr(s, '/')) {
 		return NULL;
 	}