[BUGFIX] Media element not working with FAL

With FAL the path to a file is no longer used,
instead the UID to the specific file is used,
prefixed with "file:"

This patch just adds a check if the filename
starts with "file:" and if so load the specific FileObject
to retrive the url. This check is done before all others,
because FAL should be the default file handler.
Additionally use explode() first to get the filename
if an editor adds (non used)
link parameters: file:740 _blank media-title

This fixes also the problem with audio files mentioned in #39416,
using the same patch.

Resolves: #41280
Related: #39416
Releases: 6.0, 6.1
Change-Id: Ibec6cefda54b6e136c0d5ae43c67ef2eea3b1bb8
Reviewed-on: https://review.typo3.org/19002
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn