Description:
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When we try to create a PHAR archive, and the directory, where we want to save it does not exist, PHAR complains about invalid file extension, instead of informing that there is a problem with accessing the requested location. This is a bit confusing.

Test script:
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<?php
// assume that "./dummy/" does not exist.
$phar = new Phar('./dummy/archive.phar');

Expected result:
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Cannot create phar './dummy/archive.phar', invalid path in pharbuild.php on line 2
(or something like that)

Actual result:
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UnexpectedValueException: Cannot create phar './dummy/archive.phar', file extension (or combination) not recognised in pharbuild.php on line 2