Fix cart update field enter on submit for IE

Fix for issue #11811
https://github.com/woothemes/woocommerce/issues/11811

IE handles hitting <ENTER> on an input field differently than
Chrome or Firefox in that it finds the nearest submit button
and fires the event from it instead of the actual text field
from which the user hit <ENTER>.

This commit catches the <ENTER> key event before the submit happens
and forces the cart_submit handling on that event instead.

assets/js/frontend/cart.js

@@ -267,6 +267,7 @@ jQuery( function( $ ) {
 		 */
 		init: function() {
 			this.update_cart_totals    = this.update_cart_totals.bind( this );
+			this.input_keypress        = this.input_keypress.bind( this );
 			this.cart_submit           = this.cart_submit.bind( this );
 			this.submit_click          = this.submit_click.bind( this );
 			this.apply_coupon          = this.apply_coupon.bind( this );
@@ -282,6 +283,10 @@ jQuery( function( $ ) {
 				'click',
 				'div.woocommerce > form input[type=submit]',
 				this.submit_click );
+			$( document ).on(
+				'keypress',
+				'div.woocommerce > form input[type=number]',
+				this.input_keypress );
 			$( document ).on(
 				'submit',
 				'div.woocommerce:not(.widget_product_search) > form',
@@ -352,15 +357,40 @@ jQuery( function( $ ) {
 			} );
 		},
 
+		/**
+		 * Handle the <ENTER> key for quantity fields.
+		 *
+		 * @param {Object} evt The JQuery event
+		 *
+		 * For IE, if you hit enter on a quantity field, it makes the
+		 * document.activeElement the first submit button it finds.
+		 * For us, that is the Apply Coupon button. This is required
+		 * to catch the event before that happens.
+		 */
+		input_keypress: function( evt ) {
+
+			// Catch the enter key and don't let it submit the form.
+			if ( 13 === evt.keyCode ) {
+				evt.preventDefault();
+				this.cart_submit( evt );
+			}
+		},
+
 		/**
 		 * Handle cart form submit and route to correct logic.
 		 *
 		 * @param {Object} evt The JQuery event
 		 */
 		cart_submit: function( evt ) {
-			var $form = $( evt.currentTarget );
 			var $submit = $( document.activeElement );
 			var $clicked = $( 'input[type=submit][clicked=true]' );
+			var $form = $( evt.currentTarget );
+
+			// For submit events, currentTarget is form.
+			// For keypress events, currentTarget is input.
+			if ( ! $form.is( 'form' ) ) {
+				$form = $( evt.currentTarget ).parents( 'form' );
+			}
 
 			if ( 0 === $form.find( '.shop_table.cart' ).length ) {
 				return;