patch 8.1.0300: the old window title might be freed twice

Problem:    The old window title might be freed twice. (Dominique Pelle)
Solution:   Do not free "oldtitle" in a signal handler but set a flag to have
            it freed later.

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    300,
 /**/
     299,
 /**/