Fix reading Wii FST size (for real this time)

Avoid the consequences in the unlikely event the path includes a %.

read_size remained 0 when the "Read beyond end of disc" error occurs,
which made the while (nbytes) loop never end. As a fix, SeekToCluster
now explicitly sets available to 0 when the error occurs, and Read
checks for it.

GC games with long names store two variations of the name in
opening.bnr. This makes the shorter of those names available.
For volumes other than GC discs, prefer_long is ignored.

VolumeGC: Check that opening.bnr size matches type

ISOFile and GameFile were using IsWiiDisc() and IsWadFile() to set
an enum value. The volume might as well return an enum directly.

I increased the Qt CACHE_REVISION because m_platform now is saved as u32
instead of int, but increasing the wx CACHE_REVISION is not necessary.

I tried to change messages that contained instructions for users,
while avoiding messages that are so technical that most users
wouldn't understand them even if they were in the right language.

The old code would accept files with BNR1 length and BNR2 type, which
can be a problem when GetNames tries to read the extra BNR2 strings.