fix segfault in libardour unit-tests (possible crash in mackie sf)

diff --git a/libs/surfaces/mackie/surface.cc b/libs/surfaces/mackie/surface.cc
index 274f2b42ea055af4f6e889b181e99db055035241..6941c68d29dbf93feedc292f6bfabcf6c87e9033 100644 (file)
--- a/libs/surfaces/mackie/surface.cc
+++ b/libs/surfaces/mackie/surface.cc
@@ -384,7 +384,9 @@ Surface::setup_master ()
        }
 
        if (!m) {
-               _master_fader->set_control (boost::shared_ptr<AutomationControl>());
+               if (_master_fader) {
+                       _master_fader->set_control (boost::shared_ptr<AutomationControl>());
+               }
                master_connection.disconnect ();
                return;
        }