MINOR Only setting form state if form element is available in 'ss-ui-button'

admin/javascript/ssui.core.js

@@ -26,10 +26,12 @@
 			.click(function() {
 				var form = this.form;
 				// forms don't natively store the button they've been triggered with
+				if(form) {
 					form.clickedButton = this;
 					// Reset the clicked button shortly after the onsubmit handlers
 					// have fired on the form
 					setTimeout(function() {form.clickedButton = null;}, 10);
+				}
 			});
 
 			this._super();