[-] FO : Prevent unsassigned category id, thans @PrestaCaptainFLAM

controllers/front/ProductController.php

@@ -158,7 +158,7 @@ class ProductControllerCore extends FrontController
 							$this->category = new Category($regs[5], (int)$this->context->cookie->id_lang);
 					}
 				}
-				else
+				if ( ! isset($this->category))
 					// Set default product category
 					$this->category = new Category($this->product->id_category_default, (int)$this->context->cookie->id_lang);
 			}