Upstream Patch for Unordered

Prevent erroneous copying of groups data, update max load to properly propagate

Signed-off-by: Michael Nosthoff <buildroot@heine.tech>
Upstream: https://github.com/boostorg/unordered/commit/067884a4e213352e7c81c441f1453c54735c39f3
diff --git a/include/boost/unordered/detail/foa/core.hpp b/include/boost/unordered/detail/foa/core.hpp
index 239d05d3..7ae9f2c8 100644
--- a/boost/unordered/detail/foa/core.hpp
+++ b/boost/unordered/detail/foa/core.hpp
@@ -1870,9 +1870,10 @@ private:
 
   void fast_copy_elements_from(const table_core& x)
   {
-    if(arrays.elements){
+    if(arrays.elements&&x.arrays.elements){
       copy_elements_array_from(x);
       copy_groups_array_from(x);
+      size_ctrl.ml=std::size_t(x.size_ctrl.ml);
       size_ctrl.size=std::size_t(x.size_ctrl.size);
     }
   }