check if post_type exists (#34501)

* check if post_type exists

* Changelog.

Co-authored-by: barryhughes <3594411+barryhughes@users.noreply.github.com>

plugins/woocommerce/changelog/fix-new-post-type-check

@@ -0,0 +1,4 @@
+Significance: patch
+Type: tweak
+
+Resolve an error in the product tracking code by testing to see if the `post_type` query var is set before checking its value.

plugins/woocommerce/includes/tracks/events/class-wc-products-tracking.php

@@ -317,6 +317,7 @@ class WC_Products_Tracking {
 
 		if (
 			'post-new.php' === $hook &&
+			isset( $_GET['post_type'] ) &&
 			'product' === wp_unslash( $_GET['post_type'] )
 		) {
 			return 'new';