Fix bucket deletion when using keyPrefix

[josephnle]

Background

When using the keyPrefix option along with having bucket deletion enabled, the following error occurs if the key prefix does not already exist:

ServerlessError: The XML you provided was not well-formed or did not validate against our published schema

Closes #85

Proposed changes

The issue was with the emptyBucket function. With no items containing the keyPrefix, the keyPrefix logic resulted in an empty array of S3 objects being passed to the deleteObjects S3 request. This fix resolves the promise if there are no objects to delete.

[jamesmbourne]

@fernando-mc would you be able to take a look at this please? We're currently seeing the same The XML you provided was not well-formed or did not validate against our published schema error due to this.

[fernando-mc]

Just cut a new release. This should be included in v2.6.0 @jamesmbourne @josephnle