patch 8.0.1408: crash in setqflist()

Problem:    Crash in setqflist().
Solution:   Check for string to be NULL. (Dominique Pelle, closes #2464)
diff --git a/src/version.c b/src/version.c
index c384ff0..ed86ef6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1408,
+/**/
     1407,
 /**/
     1406,