Wrong URL extraction for multi-line strings inside PO files

### Description

Extracting PO header values spread across multiple lines does not work and only considers the individual lines.

### How To Reproduce

Run URL analysis on https://github.com/django/django/blob/97c05a64ca87253e9789ebaab4b6d20a1b2370cf/django/contrib/admin/locale/en_GB/LC_MESSAGES/django.po

This will report `http://www.transifex.com/django/` as the URL instead of the full one, which would be `http://www.transifex.com/django/django/language/en_GB/`.

### System configuration

* What OS are you running on? Linux
* What version of scancode-toolkit was used to generate the scan file? 32.2.1
* What installation method was used to install/run scancode? (pip/source download/other) pip