Fixed initial tax rate settings pagination

Pagination need to be set up to 1, since is first page.
This fix a bug where is impossible to insert rates when don't have any rate saved before.

cc @mikejolley

assets/js/admin/settings-views-html-settings-tax.js

@@ -84,7 +84,9 @@
 				per_page: data.limit,
 				page: data.page,
 				initialize: function() {
-					this.qty_pages = Math.ceil( _.toArray( this.model.get( 'rates' ) ).length / this.per_page );
+					var qty_pages = Math.ceil( _.toArray( this.model.get( 'rates' ) ).length / this.per_page );
+
+					this.qty_pages = 0 === qty_pages ? 1 : qty_pages;
 					this.page = this.sanitizePage( data.page );
 
 					this.listenTo( this.model, 'change:rates', this.setUnloadConfirmation );
@@ -107,7 +109,7 @@
 					var rates       = this.model.getFilteredRates(),
 						qty_rates   = _.size( rates ),
 						qty_pages   = Math.ceil( qty_rates / this.per_page ),
-						first_index = this.per_page * ( this.page - 1),
+						first_index = 0 === qty_rates ? 0 : this.per_page * ( this.page - 1 ),
 						last_index  = this.per_page * this.page,
 						paged_rates = _.toArray( rates ).slice( first_index, last_index ),
 						view        = this;