Don't set foreground of null objects.

I should probably fix this is a nicer way, but this works.

Change-Id: I87ba4cb91d4fc99e3e2a00dde4ca909070150c9f
Reviewed-on: http://gerrit.dmdirc.com/3758
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager