patch 9.0.0335: checks for Dictionary argument often give a vague error

Problem:    Checks for Dictionary argument often give a vague error message.
Solution:   Give a useful error message. (Yegappan Lakshmanan, closes #11009)
diff --git a/src/dict.c b/src/dict.c
index 58fd68a..874b823 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -1578,11 +1578,9 @@
 		|| check_for_string_or_number_arg(argvars, 1) == FAIL))
 	return;
 
-    if (argvars[0].v_type != VAR_DICT)
-    {
-	emsg(_(e_dictionary_required));
+    if (check_for_dict_arg(argvars, 0) == FAIL)
 	return;
-    }
+
     if (argvars[0].vval.v_dict == NULL)
 	return;