fixed erase_if(x,f) return value calculation

include/boost/unordered/detail/foa/concurrent_table.hpp

@@ -555,14 +555,17 @@ public:
   {
     auto        lck=shared_access();
     auto        hash=this->hash_for(x);
-    return (std::size_t)unprotected_internal_visit(
+    std::size_t res=0;
+    unprotected_internal_visit(
       group_exclusive{},x,this->position_for(hash),hash,
       [&,this](group_type* pg,unsigned int n,element_type* p)
       {
         if(f(cast_for(group_exclusive{},type_policy::value_from(*p)))){
           super::erase(pg,n,p);
+          res=1;
         }
       });
+    return res;
   }
 
   template<typename F>