cli: fix return value of package_cmd().

It's a bug revealed by commit 446e774 "cli: properly unload package
before quit".  The current code would exit with value 1 even if
uci_export() succceeded.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

cli.c

@@ -305,10 +305,13 @@ static int package_cmd(int cmd, char *tuple)
 		}
 		if (uci_commit(ctx, &ptr.p, false) != UCI_OK) {
 			cli_perror();
+			goto out;
 		}
 		break;
 	case CMD_EXPORT:
-		uci_export(ctx, stdout, ptr.p, true);
+		if (uci_export(ctx, stdout, ptr.p, true) != UCI_OK) {
+			goto out;
+		}
 		break;
 	case CMD_SHOW:
 		if (!(ptr.flags & UCI_LOOKUP_COMPLETE)) {
@@ -333,6 +336,8 @@ static int package_cmd(int cmd, char *tuple)
 		break;
 	}
 
+	ret = 0;
+
 out:
 	if (ptr.p)
 		uci_unload(ctx, ptr.p);