adafruit_portalbase: set_text_color hits exception when label is None

[flavio-fernandes]

When trying to use code from https://learn.adafruit.com/matrix-portal-new-guide-scroller/code-the-matrix-portal
I hit the following exception:

code.py output:
Preloading font glyphs: 0123456789
obtaining time from adafruit.io server...
Connecting to AP ffiot
Getting time from IP address
New Hour, fetching new data...
Retrieving data...Obtaining guide info for guide 0...
Guide Title Adafruit Neo Trinkey
Traceback (most recent call last):
  File "code.py", line 104, in <module>
  File "code.py", line 77, in get_guide_info
  File "adafruit_portalbase/__init__.py", line 310, in set_text_color
AttributeError: 'NoneType' object cannot assign attribute 'color'

That is happening because self._text[index]["label"] may be None and code is not accounting for that.