Fix that exceptions in ReceivePack cause Invalid Channel 101 exceptions

Fix that exceptions in ReceivePack cause Invalid Channel 101 exceptions

When during a PushOperation the server hits an exception different from
UnpackException the JGit server behaved wrong. That kind of exceptions
are handled so late that the connection is already released and the
information whether to talk sideband to the client is lost. In detail:
ReceivePack.receive() will call release() and that will reset the
capabilities. But later on the stack in ReceivePackServlet.doPost() it
is tried to send a response to client now with reset capabilities (no
sideband!).

Change-Id: I0a609acc6152ab43b47a93d712deb65bb1105f75
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>