Do not assign the network name to network status buffers.

This fixes Issue #98 (https://github.com/sandsmark/QuasselDroid/issues/98) which was caused by the fact that the Quassel core decides whether or not to insert a message into a buffer (and therefore create a new buffer if it does not exist) by whether the buffer name is the empty string.  The proper Quassel client always keeps the buffer name for status buffers set to the empty string, so QuasselDroid should too.