fix(connection): set $hasHandler on promises returned from openSet()

Re: #5229

lib/connection.js

@@ -328,6 +328,8 @@ Connection.prototype.open = function() {
     });
   });
 
+  // Monkey-patch `.then()` so if the promise is handled, we don't emit an
+  // `error` event.
   var _then = promise.then;
   promise.then = function(resolve, reject) {
     promise.$hasHandler = true;
@@ -584,6 +586,15 @@ Connection.prototype.openSet = function(uris, database, options, callback) {
       resolve();
     });
   });
+
+  // Monkey-patch `.then()` so if the promise is handled, we don't emit an
+  // `error` event.
+  var _then = promise.then;
+  promise.then = function(resolve, reject) {
+    promise.$hasHandler = true;
+    return _then.call(promise, resolve, reject);
+  };
+
   return promise;
 };