Skip directories in zip generation, empty dirs won't get archived

This seems ok as we currently rely on git generating archives which does
not archive empty directories either.

src/Composer/Package/Archiver/ArchivableFilesFinder.php

@@ -25,7 +25,7 @@ use Symfony\Component\Finder;
  *
  * @author Nils Adermann <naderman@naderman.de>
  */
-class ArchivableFilesFinder
+class ArchivableFilesFinder extends \IteratorIterator
 {
     /**
      * @var Symfony\Component\Finder\Finder
@@ -66,13 +66,24 @@ class ArchivableFilesFinder
             })
             ->ignoreVCS(true)
             ->ignoreDotFiles(false);
+
+        parent::__construct($this->finder->getIterator());
     }
 
-    /**
+    public function next()
-     * @return Symfony\Component\Finder\Finder
-     */
-    public function getIterator()
     {
-        return $this->finder->getIterator();
+        do {
+            $this->getInnerIterator()->next();
+        } while ($this->getInnerIterator()->valid() && $this->getInnerIterator()->current()->isDir());
+    }
+
+    public function current()
+    {
+        return $this->getInnerIterator()->current();
+    }
+
+    public function valid()
+    {
+        return $this->getInnerIterator()->valid();
     }
 }

src/Composer/Package/Archiver/PharArchiver.php

@@ -37,7 +37,7 @@ class PharArchiver implements ArchiverInterface
         try {
             $phar = new \PharData($target, null, null, static::$formats[$format]);
             $files = new ArchivableFilesFinder($sources, $excludes);
-            $phar->buildFromIterator($files->getIterator(), $sources);
+            $phar->buildFromIterator($files, $sources);
             return $target;
         } catch (\UnexpectedValueException $e) {
             $message = sprintf("Could not create archive '%s' from '%s': %s",

tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php

@@ -169,7 +169,7 @@ class ArchivableFilesFinderTest extends \PHPUnit_Framework_TestCase
     protected function getArchivableFiles()
     {
         $files = array();
-        foreach ($this->finder->getIterator() as $file) {
+        foreach ($this->finder as $file) {
             if (!$file->isDir()) {
                 $files[] = preg_replace('#^'.preg_quote($this->sources, '#').'#', '', $file->getRealPath());
             }