Returns the entry[aq]s filename path.
Note that the filesystem encoding may not be known and the conversion to
UTF-8 could in very rare cases cause this to return an invalid path.
Therefore it[aq]s always safest to access the file over its
ALLEGRO_FS_ENTRY(3) and not the path.
On success returns a read only string which you must not modify or
Returns NULL on failure.
Note: prior to 5.1.5 it was written: "...
the path will not be an absolute path if the entry wasn[aq]t created
from an absolute path".
This is no longer true.