Mixer: Don't process (dis)connection notifications from JACK while destroying chain.

mixer/src/Chain.C

@@ -86,6 +86,7 @@ extern char *instance_name;
 Chain::Chain ( ) : Fl_Group( 0, 0, 100, 100, "")
 
 {
+    _deleting = false;
     _engine = NULL;
 
     int X = 0;
@@ -171,6 +172,8 @@ Chain::~Chain ( )
 
     log_destroy();
 
+    _deleting = true;
+
     engine()->lock();
 
     /* if we leave this up to FLTK, it will happen after we've
@@ -836,6 +839,9 @@ Chain::port_connect ( jack_port_id_t a, jack_port_id_t b, int connect, void *v )
 void
 Chain::port_connect ( jack_port_id_t a, jack_port_id_t b, int connect )
 {
+    if ( _deleting )
+        return;
+
     /* this is called from JACK non-RT thread... */
    
     if ( jack_port_is_mine( engine()->jack_client(), jack_port_by_id( engine()->jack_client(), a ) ) ||

mixer/src/Chain.H

@@ -54,6 +54,8 @@ class Chain : public Fl_Group, public Loggable {
 
     Fl_Callback *_configure_outputs_callback;
     void *_configure_outputs_userdata;
+    
+    bool _deleting;
 
 private: