adl: Immediately check result after opening file
adl: Immediately check result after opening file

In load(), a call to filesize() using the stream slipped between
open() and the check, so the check was too late. Fix that by
splitting the check for f and fileSize into two independant if
statements.

Fixes: ae1f95e6bcc3 ("adl: Sync with latest ScummVM code")

adplug/adplug,adplug/adplug