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/time.c b/src/time.c
index c28e7a9..d97c56e 100644
--- a/src/time.c
+++ b/src/time.c
@@ -872,12 +872,10 @@
     msec = (long)tv_get_number(&argvars[0]);
     if (argvars[2].v_type != VAR_UNKNOWN)
     {
-	if (argvars[2].v_type != VAR_DICT
-				   || (dict = argvars[2].vval.v_dict) == NULL)
-	{
-	    semsg(_(e_invalid_argument_str), tv_get_string(&argvars[2]));
+	if (check_for_nonnull_dict_arg(argvars, 2) == FAIL)
 	    return;
-	}
+
+	dict = argvars[2].vval.v_dict;
 	if (dict_has_key(dict, "repeat"))
 	    repeat = dict_get_number(dict, "repeat");
     }