fix: improve resilience of stop

Author: jacobheun

src/index.js

@@ -111,7 +111,7 @@ class Switch extends EE {
     series([
       (cb) => each(this.muxedConns, (conn, cb) => {
         // If the connection was destroyed while we are hanging up, continue
-        if (conn === undefined) {
+        if (!conn) {
           return cb()
         }