Check if the avatar exists before trying to delete it.
Check if the avatar exists before trying to delete it.

Fixes http://status.net/trac/ticket/1868

znarf/statusnet-ladistribution,bankonme/gnu-social,chimo/social,zh/statusnet,charlycoste/StatusNet,brion/StatusNet,brion/StatusNet,csarven/statusnet,sikevux/bsk-social,furtherfield/gnu-social,minmb/statusnet,shashi/StatusNet,znarf/statusnet-ladistribution,gnusocial/mainline,minmb/statusnet,gnusocial/mainline,brion/StatusNet,bankonme/gnu-social,csarven/statusnet,csarven/statusnet,zh/statusnet,charlycoste/StatusNet,zcopley/zcopleys-statusnet-clone,Piratas/tortuga,foocorp/gnu-social,eXcomm/gnu-social,furtherfield/gnu-social,sikevux/bsk-social,d3vgru/StatusNet,faulteh/gnu-social,foocorp/gnu-social,xebia/statusnet-oauth2,eXcomm/gnu-social,zh/statusnet,xebia/statusnet-oauth2,csarven/statusnet,gnusocial/mainline,faulteh/gnu-social,chimo/social,minmb/statusnet,Piratas/tortuga,UngPirat/freesocial,bankonme/gnu-social,Piratas/tortuga,sikevux/bsk-social,UngPirat/freesocial,faulteh/gnu-social,bankonme/gnu-social,shashi/StatusNet,Piratas/tortuga,znarf/statusnet-ladistribution,gnusocial/mainline,charnimda/lgbtpzn-social,charnimda/lgbtpzn-social,faulteh/gnu-social,sikevux/bsk-social,zcopley/zcopleys-statusnet-clone,zcopley/zcopleys-statusnet-clone,UngPirat/freesocial,eXcomm/gnu-social,zcopley/StatusNet,furtherfield/gnu-social,chimo/social,studio666/gnu-social,studio666/gnu-social,charnimda/lgbtpzn-social,furtherfield/gnu-social,eXcomm/gnu-social,xebia/statusnet-oauth2,studio666/gnu-social,d3vgru/StatusNet,shashi/StatusNet,d3vgru/StatusNet,foocorp/gnu-social,studio666/gnu-social,zcopley/StatusNet,zcopley/StatusNet,charlycoste/StatusNet