Fix some invalid iterator uses

This fixes #96. When the last user in a partyline channel is deleted, the
channel is deleted, too. This invalidates the iterator used in OnDeleteUser().
This fix is to increase the iterator before the channel can be deleted.

After the above fix, znc still crashed due to another broken use of iterators.
When a network is deleted, it takes all its clients with it (why aren't they
just moved into the "no network"-state?"). However, deleting a CClient removes
it from the network's list of clients via CClient::Disconnect(). This resulted
in another invalid use of iterators.

Signed-off-by: Uli Schlachter <psychon@znc.in>

src/IRCNetwork.cpp

@@ -181,8 +181,8 @@ CIRCNetwork::~CIRCNetwork() {
 	}
 
 	// Delete clients
-	for (vector<CClient*>::const_iterator it = m_vClients.begin(); it != m_vClients.end(); ++it) {
-		CZNC::Get().GetManager().DelSockByAddr(*it);
+	while (!m_vClients.empty()) {
+		CZNC::Get().GetManager().DelSockByAddr(m_vClients[0]);
 	}
 	m_vClients.clear();