Fixed problem where RFs would sometimes not be displayed
Fixed problem where RFs would sometimes not be displayed

Under certain conditions the AttrDict holding the RFs would not
behave correctly, preventing attribute access from working. This
commit now uses the dictionary get method, which still works under
these conditions. We should still investigate, why the AttrDict
misbehaved under these circumstances (measuring RFs after loading
a snapshot).

ioam/topographica,Tasignotas/topographica_mirror,ioam/topographica,ioam/topographica,Tasignotas/topographica_mirror,Tasignotas/topographica_mirror,Tasignotas/topographica_mirror,mjabri/topographica,ioam/topographica,mjabri/topographica,Tasignotas/topographica_mirror,mjabri/topographica,ioam/topographica,mjabri/topographica,mjabri/topographica