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/buffer.c b/src/buffer.c
index bc5dd5b..328c2b3 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -888,8 +888,13 @@
 	di->di_tv.v_type = VAR_NUMBER;
 	di->di_tv.v_lock = VAR_FIXED;
 	di->di_tv.vval.v_number = 0;
-	dict_add(buf->b_vars, di);
-	buf->b_changedtick = &di->di_tv.vval.v_number;
+	if (dict_add(buf->b_vars, di) == OK)
+	    buf->b_changedtick = &di->di_tv.vval.v_number;
+	else
+	{
+	    vim_free(di);
+	    buf->b_changedtick = &buf->b_ct_val;
+	}
     }
     else
 #endif
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,