[fix](load) fix dead loop in _handle_mem_exceed_limit function when reduce memory for load (#21886)

be/src/runtime/load_channel_mgr.cpp

@@ -371,11 +371,12 @@ void LoadChannelMgr::_handle_mem_exceed_limit() {
                     continue;
                 }
                 all_writers_mem.emplace_back(kv.second, item.first, std::move(item.second));
-                size_t pos = all_writers_mem.size() - 1;
-                tablets_mem_heap.emplace(std::get<2>(all_writers_mem[pos]).begin(),
-                                         std::get<2>(all_writers_mem[pos]).end(), pos);
             }
         }
+        for (size_t i = 0; i < all_writers_mem.size(); i++) {
+            tablets_mem_heap.emplace(std::get<2>(all_writers_mem[i]).begin(),
+                                     std::get<2>(all_writers_mem[i]).end(), i);
+        }
 
         // reduce 1/10 memory every time
         int64_t mem_to_flushed = _mem_tracker->consumption() / 10;