- Can't update an already mapped bufferData
- Can't unmap an unmapped buffer
- Disallowed illegal mapBufferRange flag combinations
- Can't flush buffer if not mapped

Change-Id: I7013f63e5db64c1016f9ce50a43d0629f0a2950e
Reviewed-on: https://swiftshader-review.googlesource.com/13788Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>