call AudioBackend::drop_device() when dropping a backend.

It is not clear that ::drop_device() is part of the same semantic operation as ::stop(), so
we call them separatey

diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index d6a511fdadab71bed5bcd0e31a0f3fb67e39dd9f..0b01f97f7a2ab4cdca473ea2566d32505097d212 100644 (file)
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -564,6 +564,7 @@ AudioEngine::drop_backend ()
 {
        if (_backend) {
                _backend->stop ();
+        _backend->drop_device();
                _backend.reset ();
        }
 }