patch 8.0.0595: Coverity warning for not checking return value

Problem:    Coverity warning for not checking return value of dict_add().
Solution:   Check the return value for FAIL.
diff --git a/src/quickfix.c b/src/quickfix.c
index 0c97702..7b07f93 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4722,7 +4722,8 @@
 	    if (di != NULL)
 	    {
 		copy_tv(qi->qf_lists[qf_idx].qf_ctx, &di->di_tv);
-		dict_add(retdict, di);
+		if (dict_add(retdict, di) == FAIL)
+		    dictitem_free(di);
 	    }
 	}
 	else