Make sure ThemeConfig is non-null when loading resources

When the device boots into safemode, the theme config will end up
being null and we need to check that prior to using it to retrieve
resources for the StatusBarIconView

This fixes CYAN-5009

Change-Id: I1a90bc9f9c65cb41a6e58947bbd1b6d7728a952b
(cherry picked from commit ad6c5826)