Suggested by degasus.

Move ownership of cached_arraybases from CPMemory to VertexLoaderManager
to better match it usage.

Yet another story of games loading weird shit into registers.

For some reason, Burnout 2 would (in rare situations) load invalid
addresses into cp_state.array_bases. What would the real hardware
do in this situation? Who knows, Burnout 2 doesn't actually enable
the vertex array with the invalid address so nothing kinky happens.

But dolphin tries to optimise things and starts using the address
as soon as it is loaded into memory. This causes GetPointer (which is
now much more vocal) to throw an error.

The Fix:  We don't call GetPointer until we are sure the vertex array
has been enabled.

This state will be used to calculate sizes for skipping over commands on
a separate thread.  An alternative to having these state variables would
be to have the preprocessor stash "state as we go" somewhere, but I
think that would be much uglier.

GetVertexSize now takes an extra argument to determine which state to
use, as does FifoCommandRunnable, which calls it.  While I'm modifying
FifoCommandRunnable, I also change it to take a buffer and size as
parameters rather than using g_pVideoData, which will also be necessary
later.  I also get rid of an unused overload.