fix: sanitize n_colors

Author: willdunklin

src/e3sm_compareview/view_manager.py

@@ -194,7 +194,18 @@ def update_color_preset(self, name, invert, log_scale, n_colors=255):
             self.lut.MapControlPointsToLogSpace()
             self.lut.UseLogScale = 1
 
-        self.lut.NumberOfTableValues = n_colors
+        # VNumberInput can transiently emit None/invalid while editing.
+        # Keep the LUT update resilient by clamping to a valid integer range.
+        resolved_n_colors = n_colors if n_colors is not None else self.config.n_colors
+        try:
+            resolved_n_colors = int(resolved_n_colors)
+        except (TypeError, ValueError):
+            resolved_n_colors = 255
+        resolved_n_colors = max(2, min(255, resolved_n_colors))
+        if self.config.n_colors != resolved_n_colors:
+            self.config.n_colors = resolved_n_colors
+
+        self.lut.NumberOfTableValues = resolved_n_colors
 
         self.config.lut_img = lut_to_img(self.lut)