When a 32-bit cursor has the same size as an 8- or 16-bit cursor,
the mouse surfaces were not being regenerated even though the
32-bit cursors have a different memory requirement. This lead to
memory corruption as an inappropriate surface would be used for
the other type of cursor.
The shoe-horned 32-bit cursor support is clearly showing its
scrappy nature here and probably ought to be revisited in the
future if the SurfaceSdl graphics manager sticks around.
Fixes Trac#10349, Trac#10350, Trac#10351.