*: remove a few more cases of argc usage. -89 bytes.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/df.c b/coreutils/df.c
index a0e6fe0..11a7398 100644
--- a/coreutils/df.c
+++ b/coreutils/df.c
@@ -35,7 +35,7 @@
 #endif
 
 int df_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int df_main(int argc, char **argv)
+int df_main(int argc UNUSED_PARAM, char **argv)
 {
 	unsigned long blocks_used;
 	unsigned blocks_percent_used;
@@ -105,7 +105,7 @@
 
 	mount_table = NULL;
 	argv += optind;
-	if (optind >= argc) {
+	if (!argv[0]) {
 		mount_table = setmntent(bb_path_mtab_file, "r");
 		if (!mount_table)
 			bb_perror_msg_and_die(bb_path_mtab_file);