In {rB0ef8a6179d2a773b2570352bd0cb7eb18b666da2} the parameter name was
changed to match the header declaration (slot) but it missed updating
the variable name inside the function correctly in one instance.
This prevents slot 0 from being cleared if the last slot to be rendered
was not also 0.
Differential Revision: https://developer.blender.org/D15620