patch 8.1.0388: Coverity complains about possible NULL pointer use

Problem:    Coverity complains about possible NULL pointer use.
Solution:   Use get_tv_string() instead of get_tv_string_chk().
diff --git a/src/version.c b/src/version.c
index 9b2e81b..dce4643 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    388,
+/**/
     387,
 /**/
     386,