list-objects-filter-options: move error check up

Move the check that filter_options->choice is set to higher in the call
stack. This can only be set when the gentle parse function is called
from one of the two call sites.

This is important because in an upcoming patch this may or may not be an
error, and whether it is an error is only known to the
parse_list_objects_filter function.

Signed-off-by: Matthew DeVore <matvore@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

list-objects-filter-options.c

@@ -35,11 +35,8 @@ static int gently_parse_list_objects_filter(
 {
 	const char *v0;
 
-	if (filter_options->choice) {
-		strbuf_addstr(
-			errbuf, _("multiple filter-specs cannot be combined"));
-		return 1;
-	}
+	if (filter_options->choice)
+		BUG("filter_options already populated");
 
 	if (!strcmp(arg, "blob:none")) {
 		filter_options->choice = LOFC_BLOB_NONE;
@@ -185,6 +182,8 @@ int parse_list_objects_filter(struct list_objects_filter_options *filter_options
 			      const char *arg)
 {
 	struct strbuf buf = STRBUF_INIT;
+	if (filter_options->choice)
+		die(_("multiple filter-specs cannot be combined"));
 	filter_options->filter_spec = strdup(arg);
 	if (gently_parse_list_objects_filter(filter_options, arg, &buf))
 		die("%s", buf.buf);