[http_request] Prevent double update task launch

Guard against launching a second FreeRTOS update task while one is
already running. Without this, calling update() twice (e.g. from both
the polling interval and the initial check interval) could spawn two
concurrent tasks both writing to the same UpdateInfo.

With the single-defer structure from the race fix PR, clearing the
handle only needs to happen in one place — at the top of the deferred
lambda, before any other work.

esphome/components/http_request/update/http_request_update.cpp

@@ -74,6 +74,10 @@ void HttpRequestUpdate::update() {
   }
   this->cancel_interval(INITIAL_CHECK_INTERVAL_ID);
 #ifdef USE_ESP32
+  if (this->update_task_handle_ != nullptr) {
+    ESP_LOGW(TAG, "Update check already in progress");
+    return;
+  }
   xTaskCreate(HttpRequestUpdate::update_task, "update_task", 8192, (void *) this, 1, &this->update_task_handle_);
 #else
   this->update_task(this);
@@ -204,6 +208,9 @@ defer:
   // both success and error paths to avoid multiple std::function instantiations.
   // Lambda captures only 2 pointers (8 bytes) — fits in std::function SBO on supported toolchains.
   this_update->defer([this_update, result]() {
+#ifdef USE_ESP32
+    this_update->update_task_handle_ = nullptr;
+#endif
     if (result->error_str != nullptr) {
       this_update->status_set_error(result->error_str);
       delete result;