Merge pull request #5043 from spitimage/fix4850

Don't rollback twice on connection error. Fixes issue #4850.

lib/sequelize.js

@@ -1236,8 +1236,8 @@ Sequelize.prototype.transaction = function(options, autoCallback) {
           });
         });
       }).catch(function(err) {
-        // If an error occured while commiting a transaction do not try to rollback the transaction
-        if (transaction.finished === 'commit') {
+        // If the transaction has already finished (commit, rollback, etc), reject with the original error
+        if (transaction.finished) {
           reject(err);
         } else {
           transaction.rollback().finally(function () {