Add overflow check

test/scan-test.cc

@@ -63,6 +63,9 @@ TEST(scan_test, read_hex) {
   unsigned n = 0;
   fmt::scan("2a", "{:x}", n);
   EXPECT_EQ(n, 42);
+  auto num_digits = std::numeric_limits<unsigned>::digits / 4;
+  EXPECT_THROW_MSG(fmt::scan(fmt::format("1{:0{}}", 0, num_digits), "{:x}", n),
+                   fmt::format_error, "number is too big");
 }
 
 TEST(scan_test, read_string) {