Show *.po header in page footer if [project] footer is empty

[Jun Omae]

If [project] footer in trac.ini is empty, Trac wrongly shows *.po header in the page footer.

Real world examples → ​google:'"Powered by Trac" "Project-Id-Version: Trac" "Report-Msgid-Bugs-To: trac-dev@googlegroups.com POT-Creation-Date"'

trac/web/chrome.py

@@ -709 +709 @@
             'admin_href': admin_href,
             'admin_trac_url': self.env.project_admin_trac_url,
         }
+        footer = self.env.project_footer
         d['chrome'] = {
-            'footer': Markup(translation.gettext(self.env.project_footer))
+            'footer': Markup(footer and translation.gettext(footer))
         }
         if req:
             d['chrome'].update(req.chrome)

I'll commit it right away.