don't crash on empty subpaths

lib/elements/element.py

@@ -29,6 +29,10 @@ class Patch:
         else:
             raise TypeError("Patch can only be added to another Patch")
 
+    def __len__(self):
+        # This method allows `len(patch)` and `if patch:
+        return len(self.stitches)
+
     def add_stitch(self, stitch):
         self.stitches.append(stitch)
 
@@ -36,7 +40,6 @@ class Patch:
         return Patch(self.color, self.stitches[::-1])
 
 
-
 class Param(object):
     def __init__(self, name, description, unit=None, values=[], type=None, group=None, inverse=False, default=None, tooltip=None, sort_index=0):
         self.name = name

lib/elements/stroke.py

@@ -97,6 +97,11 @@ class Stroke(EmbroideryElement):
         # TODO: use inkstitch.stitches.running_stitch
 
         patch = Patch(color=self.color)
+
+        # can't stitch a single point
+        if len(emb_point_list) < 2:
+            return patch
+
         p0 = emb_point_list[0]
         rho = 0.0
         side = 1
@@ -156,6 +161,7 @@ class Stroke(EmbroideryElement):
             else:
                 patch = self.stroke_points(path, self.zigzag_spacing / 2.0, stroke_width=self.stroke_width)
 
-            patches.append(patch)
+            if patch:
+                patches.append(patch)
 
         return patches