🐛 fixed a logical error

Treated the size of the range as the number of thousand separators.
This logical error yielded a negative value for written_bytes and
eventually an infinite loop, as written_bytes was converted to an
unsigned value.

src/json.hpp.re2c

@@ -6648,7 +6648,8 @@ class basic_json
             {
                 const auto end = std::remove(m_buf.begin(), m_buf.begin() + written_bytes, thousands_sep);
                 std::fill(end, m_buf.end(), '\0');
-                written_bytes -= (m_buf.end() - end);
+                assert((end - m_buf.begin()) <= written_bytes);
+                written_bytes = (end - m_buf.begin());
             }
 
             // convert decimal point to '.'