1.7.1dev: merge [17881] from 1.6-stable (refs #13864)

git-svn-id: http://trac.edgewall.org/intertrac/log:/trunk@17882 af82e41b-90c4-0310-8c96-b1721e28e2e2

Author: jomae

trac/mimeview/pygments.py

@@ -174,7 +174,9 @@ def style_defs(style):
         if default_style not in styles:
             default_style = 'trac'
         selection = req.session.get('pygments_style')
-        if selection not in styles:
+        if not selection:
+            selection = ''
+        elif selection not in styles:
             selection = default_style
         output = self._generate('html', self.EXAMPLE)
         add_script_data(req, default_style=default_style, selection=selection)