Currently if topology.get_location() doesn't find an entry in its
collection(s) it throws standard out-of-range exception which's very
hard to debug.
Also, next patches will extend this method, the introduced here if
(_current_locations.contains()) makes this future change look nicer.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
fa613285e7