activity: fix bug in case of user with no projects at all.
activity: fix bug in case of user with no projects at all.

DrXyzzy/smc,tscholl2/smc,tscholl2/smc,DrXyzzy/smc,tscholl2/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,sagemathinc/smc,sagemathinc/smc