set_text_color: check if label is None before assigning value

Make sure label of text is set before changing its color property.

Fixes: adafruit#29

Author: flavio-fernandes

adafruit_portalbase/__init__.py

@@ -307,7 +307,8 @@ def set_text_color(self, color, index=0):
         if self._text[index]:
             color = self.html_color_convert(color)
             self._text[index]["color"] = color
-            self._text[index]["label"].color = color
+            if self._text[index]["label"] is not None:
+                self._text[index]["label"].color = color
 
     def exit_and_deep_sleep(self, sleep_time):
         """