Fix to avoid overwriting the backup file of a 0.99 session when opening a session

This is equivalent to the fix applied as rev 2244 to the 2.0-ongoing branch


git-svn-id: svn://localhost/ardour2/trunk@2402 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/ardour/session_state.cc

@@ -728,6 +728,11 @@ Session::load_state (string snapshot_name)
 
 		backup_path /= snapshot_name + "-1" + statefile_suffix;
 
+		// only create a backup once
+		if (sys::exists (backup_path)) {
+			return 0;
+		}
+
 		info << string_compose (_("Copying old session file %1 to %2\nUse %2 with Ardour versions before 2.0 from now on"),
 					xmlpath.to_string(), backup_path.to_string()) 
 		     << endmsg;