Fix bug with double unload on unsuccessful dlopen

In the case of unsuccessful dlopen the failure guard is triggered
for two namespaces which leads to double unload.

Also update soinfo_free to abort in case when linker tries to free same
soinfo for the second time - this makes linker behavior less undefined.

Test: bionic-unit-tests
Bug: http://b/69787209
Change-Id: I886787ee021b050667f967bce7aa2708390886ea