add error message for invalid geometries (#216)

lib/elements/fill.py

@@ -120,7 +120,10 @@ class Fill(EmbroideryElement):
         poly_ary.sort(key=lambda point_list: shgeo.Polygon(point_list).area, reverse=True)
 
         polygon = shgeo.MultiPolygon([(poly_ary[0], poly_ary[1:])])
-        # print >> sys.stderr, "polygon valid:", polygon.is_valid
+
+        if not polygon.is_valid:
+            self.fatal(_("shape is not valid.  This can happen if the border crosses over itself."))
+
         return polygon
 
     def to_patches(self, last_patch):

messages.po

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2018-09-01 19:54-0400\n"
+"POT-Creation-Date: 2018-09-01 20:06-0400\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"
@@ -264,6 +264,10 @@ msgid ""
 " it bigger or delete it."
 msgstr ""
 
+#: lib/elements/fill.py:125
+msgid "shape is not valid.  This can happen if the border crosses over itself."
+msgstr ""
+
 #: lib/elements/satin_column.py:10
 msgid "Satin Column"
 msgstr ""