[http_request] Fix infinite loop when server doesn't send Content-Length header (#12480)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

esphome/components/http_request/update/http_request_update.cpp

@@ -76,6 +76,11 @@ void HttpRequestUpdate::update_task(void *params) {
 
     yield();
 
+    if (read_bytes <= 0) {
+      // Network error or connection closed - break to avoid infinite loop
+      break;
+    }
+
     read_index += read_bytes;
   }