Update pygments monkeypatch for compatibility with Pygments 2.0

Closes gh-6877

IPython/qt/console/pygments_highlighter.py

@@ -24,6 +24,7 b" def get_tokens_unprocessed(self, text, stack=('root',)):"
         for rexmatch, action, new_state in statetokens:
             m = rexmatch(text, pos)
             if m:
+                if action is not None:
                 if type(action) is _TokenType:
                     yield pos, action, m.group()
                 else: