Don't freeze when out of known nodes
Don't freeze when out of known nodes

- bitmessage could end up having no known nodes and then it would
  freeze. Now it shouldn't freeze, however it can still end up without
  known nodes until a restart in some cases (e.g. when suspending the
  computer for more then 3 days while BM is running)

hb9kns/PyBitmessage,hb9kns/PyBitmessage,timothyparez/PyBitmessage,timothyparez/PyBitmessage,debguy0x/PyBitmessage,bmng-dev/PyBitmessage,bmng-dev/PyBitmessage,hb9kns/PyBitmessage,debguy0x/PyBitmessage,bmng-dev/PyBitmessage,timothyparez/PyBitmessage,hb9kns/PyBitmessage,debguy0x/PyBitmessage,timothyparez/PyBitmessage,debguy0x/PyBitmessage