Fix some integer warnings in 64-bit builds

include/boost/beast/http/string_body.hpp

@@ -93,8 +93,7 @@ public:
         {
             if(length)
             {
-                if(*length > (
-                    std::numeric_limits<std::size_t>::max)())
+                if(static_cast<std::size_t>(*length) != *length)
                 {
                     ec = error::buffer_overflow;
                     return;