Make check_cart_items consistantly placed

Closes #6708

includes/class-wc-cart.php

@@ -1274,6 +1274,8 @@ class WC_Cart {
 				$this->apply_cart_discounts_after_tax();
 			}
 
+			do_action( 'woocommerce_after_calculate_totals', $this );
+
 			$this->set_session();
 		}
 

includes/shortcodes/class-wc-shortcode-checkout.php

@@ -205,15 +205,16 @@ class WC_Shortcode_Checkout {
 		wc_print_notices();
 
 		// Check cart has contents
-		if ( sizeof( WC()->cart->get_cart() ) == 0 )
+		if ( sizeof( WC()->cart->get_cart() ) == 0 ) {
 			return;
+		}
+
+		// Check cart contents for errors
+		do_action( 'woocommerce_check_cart_items' );
 
 		// Calc totals
 		WC()->cart->calculate_totals();
 
-		// Check cart contents for errors
-		do_action('woocommerce_check_cart_items');
-
 		// Get checkout object
 		$checkout = WC()->checkout();