minor symfony#10685 Update MimeTypeExtensionGuesser.php (marktopper)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes symfony#10685).

Discussion
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Update MimeTypeExtensionGuesser.php

Fixed bug for MimeType `image/x-ms-bmp`

Commits
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be0e362 Update MimeTypeExtensionGuesser.php

Author: fabpot

src/Symfony/Component/HttpFoundation/File/MimeType/MimeTypeExtensionGuesser.php

@@ -655,6 +655,7 @@ class MimeTypeExtensionGuesser implements ExtensionGuesserInterface
         'chemical/x-csml' => 'csml',
         'chemical/x-xyz' => 'xyz',
         'image/bmp' => 'bmp',
+        'image/x-ms-bmp' => 'bmp',
         'image/cgm' => 'cgm',
         'image/g3fax' => 'g3',
         'image/gif' => 'gif',