Skip stitch zero length row (#3054)

* fix #3052
* add one stitch for zero length row

lib/stitches/fill.py

@@ -54,6 +54,10 @@ def adjust_stagger(stitch, angle, row_spacing, max_stitch_length, staggers):
 
 def stitch_row(stitches, beg, end, angle, row_spacing, max_stitch_length, staggers, skip_last,
                enable_random_stitch_length, random_sigma, random_seed):
+    if end == beg:
+        stitches.append(Stitch(*beg, tags=('fill_row_start',)))
+        return
+
     beg = Stitch(*beg, tags=('fill_row_start',))
     end = Stitch(*end, tags=('fill_row_start',))
     stitches.append(beg)