Fix overflow check

fmt/format.h

@@ -3758,17 +3758,19 @@ template <typename Char>
 unsigned parse_nonnegative_int(const Char *&s) {
   assert('0' <= *s && *s <= '9');
   unsigned value = 0;
+  // Convert to unsigned to prevent a warning.
+  unsigned max_int = (std::numeric_limits<int>::max)();
+  unsigned big = max_int / 10;
   do {
-    unsigned new_value = value * 10 + (*s++ - '0');
-    // Check if value wrapped around.
-    if (new_value < value) {
-      value = (std::numeric_limits<unsigned>::max)();
+    // Check for overflow.
+    if (value > big) {
+      value = max_int + 1;
       break;
     }
-    value = new_value;
+    value = value * 10 + (*s - '0');
+    ++s;
   } while ('0' <= *s && *s <= '9');
   // Convert to unsigned to prevent a warning.
-  unsigned max_int = (std::numeric_limits<int>::max)();
   if (value > max_int)
     FMT_THROW(FormatError("number is too big"));
   return value;