From 98b9459535681a0c3a4739f208a32dfc50c9bfea Mon Sep 17 00:00:00 2001
From: gatecat <gatecat@ds0.me>
Date: Tue, 12 Sep 2023 18:12:07 +0200
Subject: [PATCH] fmt: Fix C++ string assertion when buf is empty

Signed-off-by: gatecat <gatecat@ds0.me>
---
 kernel/fmt.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/fmt.cc b/kernel/fmt.cc
index 69bdbb013b0..965e58ebce4 100644
--- a/kernel/fmt.cc
+++ b/kernel/fmt.cc
@@ -740,7 +740,7 @@ std::string Fmt::render() const
 				log_assert(part.width == 0 || part.padding != '\0');
 				if (part.justify == FmtPart::RIGHT && buf.size() < part.width) {
 					size_t pad_width = part.width - buf.size();
-					if (part.padding == '0' && (buf.front() == '+' || buf.front() == '-')) {
+					if (part.padding == '0' && (!buf.empty() && (buf.front() == '+' || buf.front() == '-'))) {
 						str += buf.front();
 						buf.erase(0, 1);
 					}