[2.2.x] Made versionadded/versionchanged annotations without a conten…

…t end with ".".

Regression in d2afa5e.
Backport of 5032556 from master

docs/_ext/djangodocs.py

@@ -153,7 +153,7 @@ def visit_versionmodified(self, node):
         if version_text:
             title = "%s%s" % (
                 version_text % node['version'],
-                ":" if node else "."
+                ":" if len(node) else "."
             )
             self.body.append('<span class="title">%s</span> ' % title)