Fix up custom plugin issues

openlp/core/lib/songxmlhandler.py

@@ -134,6 +134,7 @@ class SongXMLParser(object):
         ``xml``
             The XML of the song to be parsed.
         """
+        self.song_xml = None
         try:
             self.song_xml = ElementTree(
                 element=XML(unicode(xml).encode('unicode-escape')))

openlp/plugins/custom/forms/editcustomform.py

@@ -106,7 +106,7 @@ class EditCustomForm(QtGui.QDialog, Ui_customEditDialog):
         for themename in themelist:
             self.ThemeComboBox.addItem(themename)
 
-    def loadCustom(self, id, preview):
+    def loadCustom(self, id, preview=False):
         self.customSlide = CustomSlide()
         self.initialise()
         if id != 0: