When setting the Viewport Anti-Aliasing samples in the user preferences
to a lower sample count the anti-aliasing was not reset. This lead to
incorrect result as the accum buffer would still hold the values of the
larger sample count.
This fix resets the TAA when the sample count is changed.
Reviewed By: Clément Foucault
Differential Revision: https://developer.blender.org/D7728
eb23b39b7f