Replace missing .mid files with silence

This fixes a crash: missing playlist due to missing .mid,
and retains regions for missing MIDI files.

As opposed to missing Audio, we cannot use a SilentFileSource,
because MIDI files are destructive.

This also adds an API to query missing files that have been replaced
with silence to report them to the user.

1 files changed, 1 insertions, 0 deletions

diff --git a/libs/ardour/ardour/source.h b/libs/ardour/ardour/source.h
index 56e72acd42..9604062b8e 100644
--- a/libs/ardour/ardour/source.h
+++ b/libs/ardour/ardour/source.h
@@ -56,6 +56,7 @@ public:
 		Destructive = 0x80,
 		Empty = 0x100, /* used for MIDI only */
 		RF64_RIFF = 0x200,
+		Missing = 0x400, /* used for MIDI only */
 	};
 
 	typedef Glib::Threads::Mutex::Lock Lock;