error if satin column set for path with single subpath

lib/elements/satin_column.py

@@ -97,6 +97,8 @@ class SatinColumn(EmbroideryElement):
     def flattened_beziers(self):
         if len(self.csp) == 2:
             return self.simple_flatten_beziers()
+        elif len(self.csp) < 2:
+            self.fatal(_("satin column: %(id)s: at least two subpaths required (%(num)d found)") % dict(num=len(self.csp), id=self.node.get('id')))
         else:
             return self.flatten_beziers_with_rungs()
 

messages.po

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2018-06-01 20:34-0400\n"
+"POT-Creation-Date: 2018-06-10 16:01-0400\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -124,6 +124,10 @@ msgstr ""
 msgid "Inset amount (default: half of contour underlay inset)"
 msgstr ""
 
+#, python-format
+msgid "satin column: %(id)s: at least two subpaths required (%(num)d found)"
+msgstr ""
+
 msgid ""
 "One or more rails crosses itself, and this is not allowed.  Please split "
 "into multiple satin columns."