Mixer: Fix crash if user messes with the window while project is loading.

mixer/src/Mixer.C

@@ -1097,6 +1097,9 @@ Mixer::send_feedback ( void )
 int
 Mixer::handle ( int m )
 {
+    /* if user presses certain keys when project is loading it can cause a crash. Don't respond to input. */
+    if ( Project::is_opening() )
+	return 0;
     
     if ( Fl_Group::handle( m ) )
         return 1;

mixer/src/Mixer_Strip.C

@@ -1149,6 +1149,9 @@ Mixer_Strip::handle ( int m )
 {
     static int _button = 0;
 
+    if (!_chain )
+	return 0;
+    
     Logger log( this );
     
     static Fl_Widget *dragging = NULL;