ensure clients are valid when iterated over

include/TServer.h

@@ -51,10 +51,14 @@ public:
             Clients = mClients;
         }
         for (auto& Client : Clients) {
+            if (Client) [[likely]] {
                 IterationDecision Decision = std::invoke(Fn, Client);
                 if (Decision == IterationDecision::Break) {
                     break;
                 }
+            } else {
+                beammp_assert_not_reachable();
+            }
         }
     }
     template <ForEachHandler FnT>
@@ -65,7 +69,11 @@ public:
             Clients = mClients;
         }
         for (auto& Client : Clients) {
+            if (Client) [[likely]] {
                 std::invoke(Fn, Client);
+            } else {
+                beammp_assert_not_reachable();
+            }
         }
     }
     size_t ClientCount() const;