fix(lut): allow number of color to be deleted

Author: jourdain

src/e3sm_quickview/view_manager.py

@@ -165,7 +165,8 @@ def update_color_preset(self, name, invert, log_scale, n_colors=255):
             self.lut.MapControlPointsToLogSpace()
             self.lut.UseLogScale = 1
 
-        self.lut.NumberOfTableValues = n_colors
+        if n_colors is not None:
+            self.lut.NumberOfTableValues = n_colors
 
         self.config.lut_img = lut_to_img(self.lut)