Unattached quotes cause undefined array key spam

[reedy]

When reading a file with a comment not attached to a translation block, there logs get spammy

foo.po

# Foo
msgid "Foo"
msgstr "Fop"

# foo

comments.php

<?php

require_once 'vendor/autoload.php';

$parser = new PoParser\Parser();
$parser->read("foo.po");

$ php comments.php 
PHP Warning:  Undefined array key "msgid" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Parser.php on line 340
PHP Warning:  Undefined array key "msgid" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Parser.php on line 340
PHP Warning:  Undefined array key "msgid" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Parser.php on line 340
PHP Warning:  Undefined array key "msgid" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Parser.php on line 340
PHP Warning:  Undefined array key "msgid" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Entry.php on line 70
PHP Warning:  Undefined array key "msgstr" in /tmp/poparser/vendor/maxakawizard/po-parser/src/Entry.php on line 75