This should fix the problem that in LoadLocation SFLAG_INTEXTURE path gl calls 
can be made without activating context, due to isInDraw checks.

Strictly speaking this is redundant because the UnLoad before did the
job, but if we mess with the allocated memory we have to tell the
surface about that. Updating INDRAWABLE will automatically mark SYSMEM
outdated.

If we mark the sysmem copy up to date we would have to take care about
allocating it. As explained in the comment, INDRAWABLE is a saner
choice