fix silly math error

scripts/xyz_grid.py

@@ -485,7 +485,7 @@ class Script(scripts.Script):
         zs = process_axis(z_opt, z_values)
 
         # this could be moved to common code, but unlikely to be ever triggered anywhere else
-        Image.MAX_IMAGE_PIXELS = opts.img_max_size_mp * 1.1 # allow 10% overhead for margins and legend
+        Image.MAX_IMAGE_PIXELS = opts.img_max_size_mp * 1000000 * 1.1 # allow 10% overhead for margins and legend
         grid_mp = round(len(xs) * len(ys) * len(zs) * p.width * p.height / 1000000)
         if grid_mp > opts.img_max_size_mp:
             return Processed(p, [], p.seed, info=f'Error: Resulting grid would be too large ({grid_mp} MPixels) (max configured size is {opts.img_max_size_mp} MPixels)')