Usually when doing a WINED3D_MAP_DISCARD map on a buffer with a buffer object
WINED3D_LOCATION_BUFFER will already be current. However, if the previous map
on that buffer loaded WINED3D_LOCATION_SYSMEM, that's not necessarily true.
This also brings the code further in line with the corresponding code for
textures.
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>