Show IP's contributions on SpecialMobileContributions, too

Instead of an error page "not found", show the contributions of an
anonymous/IP user.

Bug: 68775
Change-Id: I1ed863cf515d362daf08391f7fabd972819601e3
(cherry picked from commit 2abcca0ca4b2e9a7043721047f7b08efabdba45c)