fix #19 missing start tag error

Author: blue-bird1

telegraph/utils.py

@@ -83,6 +83,11 @@ def handle_endtag(self, tag):
         if tag in VOID_ELEMENTS:
             return
 
+        if not len(self.parent_nodes):
+            raise InvalidHTML('"{}" missing start tag'.format(
+                tag
+            ))
+
         self.current_nodes = self.parent_nodes.pop()
 
         last_node = self.current_nodes[-1]