elf: Fix memory leak in _dl_find_object_update (bug 29062)

The count can be zero if an object has already been loaded as
an indirect dependency (so that l_searchlist.r_list in its link
map is still NULL) is promoted to global scope via RTLD_GLOBAL.

Fixes commit 5d28a896 ("elf: Add _dl_find_object function").

(cherry picked from commit 4a41fc3c)