patch 8.0.0340: not checking return valud of dict_add()

Problem:    Not checking return valud of dict_add(). (Coverity)
Solution:   Handle a failure.
diff --git a/src/version.c b/src/version.c
index 41a0321..ef71d0e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    340,
+/**/
     339,
 /**/
     338,