patch 8.1.1515: memory leak reported for sound when build with EXITFREE

Problem:    Memory leak reported for sound when build with EXITFREE.
Solution:   Free sound stuff when exiting.
diff --git a/src/version.c b/src/version.c
index 8420be6..b493377 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1515,
+/**/
     1514,
 /**/
     1513,