VideoCommon/Statistics: Use unsigned int where appropriate

Some poorly coded games are able to overflow some statistics (e.g. Jimmy Neutron: Boy Genius's title screen).
While funny, signed integer overflow is undefined behavior, and while in practice here it's extremely unlikely to cause issues, it's still better to avoid it.

DSPHLE/Zelda: Add bounds check for m_sync_voice_skip_flags in RenderAudio()

GCMemcardDirectory: Add bounds check for m_save_data

IOS/FS: Fix loading savestate while TASing

The only negative result UsesBlock can return is -1, so this change
doesn't affect anything in practice, but makes the intent a little bit
clearer.

When calling CreateDirectory for /wfs, we were passing a UID of 19,
because that is the UID /wfs is supposed to have. However,
CreateDirectory returns AccessDenied if we try to create a directory in
the root using a UID other than 0.

To fix this, let's use UID 0 to create the directory, and then change
the UID and GID afterwards using SetMetadata. This is what the ESCore
constructor does, which is the piece of code that normally creates /wfs.

When TASing, we savestate not just /tmp but also /. The code that was
added in d35fe1b didn't handle recreating / correctly.

This commit fixes the problem by skipping recreating /, which is fine
since it always exists.