Description:
------------
When using convertToExecutable() to add compression to an existing phar archive, 
if the original phar name contains full stops . the new phar.tar.gz extension is 
added to early.

eg;

proem-0.1.2.phar

becomes:

proem-0.phar.tar.gz

Test script:
---------------
#!/usr/bin/env php
<?php
require 'lib/Proem/Api/Proem.php';
$phar = new Phar('build/proem-' . Proem\Api\Proem::VERSION . '.phar');
$phar->buildFromDirectory('lib');
$phar->setStub("<?php
Phar::mapPhar('proem.phar');
require_once 'phar://proem.phar/Proem/Autoloader.php';
(new Proem\Autoloader())->registerNamespaces(['Proem' => 'lib'])->register();
__HALT_COMPILER();
?>");
$phar->convertToExecutable(Phar::TAR, Phar::GZ);

Expected result:
----------------
thorpe@dev[~/src/proem][master]+ ls -l build/
total 76
-rw-r--r-- 1 thorpe thorpe 64006 Feb  2 23:53 proem-0.1.2.phar
-rw-r--r-- 1 thorpe thorpe  8523 Feb  2 23:53 proem-0.1.2.phar.tar.gz

Actual result:
--------------
thorpe@dev[~/src/proem][master]+ ls -l build/
total 76
-rw-r--r-- 1 thorpe thorpe 64006 Feb  2 23:53 proem-0.1.2.phar
-rw-r--r-- 1 thorpe thorpe  8523 Feb  2 23:53 proem-0.phar.tar.gz