handleFiles does not correctly handle directory creation failure

[bright-tools]

in PhotoBackupService::handleFiles(), the second call to mExistingFiles.containsKey() erroneously uses bucketName as the parameter rather than bucketTargetDir and also inverts the result. This means that in the case that there is a top-level directory specified in the configuration the condition will always evaluate to true (meaning that failure to create the directory will be missed). In the case that there is no top-level directory specified, successful creation of the directory will result in an erroneous error indicating that the directory could not be created.