Fix failed assertion when end_write is called multiple times.

Bad logic, but oh well, doesn't hurt.


git-svn-id: svn://localhost/ardour2/branches/3.0@5850 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/evoral/src/Sequence.cpp

@@ -555,7 +555,11 @@ void
 Sequence<Time>::end_write(bool delete_stuck)
 {
 	write_lock();
-	assert(_writing);
+
+	if (!_writing) {
+		write_unlock();
+		return;
+	}
 
 	DUMP(format("%1% : end_write (%2% notes)\n") % this % _notes.size());