Merge XMP Metadata if dc:format tag not found

[GreyWyvern]

Type of pull request

• [X] Bug fix (involves code and configuration changes)

About

Previously extractXMPMetadata() would check for the existence of a dc:format tag with an application/pdf MIME-type value before allowing found XMP metadata to be merged with the other document details.

If the tag doesn't exist, merge the metadata anyway. If it does exist, only then check to see if it has the application/pdf MIME-type. Resolves #721.

Checklist for code / configuration changes

In case you changed the code/configuration, please read each of the following checkboxes as they contain valuable information:

• [X] Please add at least one test case (unit test, system test, ...) to demonstrate that the change is working. If existing code was changed, your tests cover these code parts as well.
• [X] Please run PHP-CS-Fixer before committing, to confirm with our coding styles. See https://github.com/smalot/pdfparser/blob/master/.php-cs-fixer.php for more information about our coding styles.
• [X] In case you fix an existing issue, please do one of the following:
  • [X] Write in this text something like fixes #1234 to outline that you are providing a fix for the issue #1234.