Skip recent sessions with empty strings for names

This can happen if the recent sessions file has new lines with no
characters on it which can be the direct loading sessions with wacky
names. For example, one that has a carriage return or newline in it.

gtk2_ardour/session_dialog.cc

@@ -778,6 +778,10 @@ SessionDialog::redisplay_recent_sessions ()
 
 		/* remove any trailing / */
 
+		if (dirname.empty()) {
+			continue;
+		}
+
 		if (dirname[dirname.length()-1] == '/') {
 			dirname = dirname.substr (0, dirname.length()-1);
 		}