The constructor leaves treeroot null when it can't find a CD001 volume
descriptor, but GetFromPath walked into it anyway - TreeEntry *entry = treeroot;
then entry->valid - so any path lookup on a failed mount dereferenced null.
Reachable from the firmware installer, which mounts whatever file it's handed
and asks for PSP_GAME/SYSDIR/UPDATE without consulting Error() first. Point it
at a PlayStation disc image, whose descriptor sits behind a Mode 2 subheader and
so fails the signature check, and PPSSPP goes down. Identify_File checks for
CD001 before reporting PSP_ISO, so the game browser was never exposed.
Return null instead, which is what the rest of the function already does for a
path that isn't there, and what every caller expects.
Henrik Rydgård
981250daf3