Add more robust logic to find the last Bar in a ScorePart

This avoids an AttributeError if the last object in a ScorePart's
barlist is not a Bar. For example, \addlyrics blocks are represented by
simple Python lists rather than Bar objects.

Fixes #69.

Author: bmjcode

ly/musicxml/xml_objs.py

@@ -96,8 +96,8 @@ def iterate_partgroup(self, group):
 
     def iterate_part(self, part):
         """The part is iterated."""
-        if part.barlist:
-            last_bar = part.barlist[-1]
+        last_bar = part.last_bar()
+        if last_bar:
             last_bar_objs = last_bar.obj_list
             part.set_first_bar(self.divisions)
             self.musxml.create_part(part.name, part.abbr, part.midi)
@@ -458,6 +458,12 @@ def extract_global_to_section(self, name):
             section.barlist.append(section_bar)
         return section
 
+    def last_bar(self):
+        """Returns the last Bar object in the score, or None if the score is empty."""
+        for obj in reversed(self.barlist):
+            if isinstance(obj, Bar):
+                return obj
+
 
 class Bar():
     """ Representing the bar/measure.