another fix to avoid frequent warnings

README.md

@@ -101,6 +101,7 @@ If the input file group is PAGE-XML (from a previous OCR-D workflow step), Eynol
   (because some other preprocessing step was in effect like `denoised`), then
   the output PAGE-XML will be based on that as new top-level (`@imageFilename`)
 
+
     ocrd-eynollah-segment -I OCR-D-XYZ -O OCR-D-SEG -P models 2022-04-05
 
 Still, in general, it makes more sense to add other workflow steps **after** Eynollah.

src/eynollah/utils/separate_lines.py

@@ -1681,7 +1681,7 @@ def do_work_of_slopes_new_curved(
             textline_con_fil = filter_contours_area_of_image(img_int_p, textline_con,
                                                              hierarchy,
                                                              max_area=1, min_area=0.0008)
-            y_diff_mean = find_contours_mean_y_diff(textline_con_fil)
+            y_diff_mean = find_contours_mean_y_diff(textline_con_fil) if len(textline_con_fil) > 1 else np.NaN
             if np.isnan(y_diff_mean):
                 slope_for_all = MAX_SLOPE
             else: