When using a tool that is not a brush, the previously used brush
preset will still be active in the tool settings, so the cursor will
draw its custom reviews.
This checks if the current active tool is a brush before drawing its
previews. If it is not a brush tools, it draws a default white cursor.
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D9418
d70cfb90e0