(Bug 5221) More S2-related uninitialized value warnings.

Use of uninitialized value in string eq at
/dreamhack/home/8103-alierak/dw/cgi-bin/LJ/S2/IconsPage.pm line 69.

Use of uninitialized value $overriding_prop_name in hash element at
/dreamhack/home/8103-alierak/dw/cgi-bin/LJ/Widget/S2PropGroup.pm line 127.

Use of uninitialized value $prop_list_class in concatenation (.) or string at
/dreamhack/home/8103-alierak/dw/cgi-bin/LJ/Widget/S2PropGroup.pm line 189.