Prevent mapped buffers from being discarded;
Prevent mapped buffers from being discarded;

We never try to do this anyway, and the unmapping code in discard
doesn't flush contents so it's better for people to unmap the
buffer themselves before calling discard.

bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr