tracker: Fix crash on handling invalid birthday dates from contacts
tracker: Fix crash on handling invalid birthday dates from contacts

If a GDateTime cannot be constructed due to the requested date being
invalid or out of range, the constructor will return null. The code was
not previously handling this.

https://bugzilla.gnome.org/show_bug.cgi?id=727944

GNOME/folks,GNOME/folks,GNOME/folks,pwithnall/folks,pwithnall/folks,pwithnall/folks