patch 8.0.0264: memory error reported by ubsan

Problem:    Memory error reported by ubsan, probably for using the string
            returned by execute().
Solution:   NUL terminate the result of execute().
diff --git a/src/version.c b/src/version.c
index 67fe69b..5431022 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    264,
+/**/
     263,
 /**/
     262,