Fix query parameter issue in notes plugin.

Closes #1392.

plugin/notes/notes.html

@@ -288,9 +288,10 @@
 						'backgroundTransition=none'
 					].join( '&' );
 
+					var urlSeparator = /?/.test(data.url) ? '&' : '?';
 					var hash = '#/' + data.state.indexh + '/' + data.state.indexv;
-					var currentURL = data.url + '?' + params + '&postMessageEvents=true' + hash;
-					var upcomingURL = data.url + '?' + params + '&controls=false' + hash;
+					var currentURL = data.url + urlSeparator + params + '&postMessageEvents=true' + hash;
+					var upcomingURL = data.url + urlSeparator + params + '&controls=false' + hash;
 
 					currentSlide = document.createElement( 'iframe' );
 					currentSlide.setAttribute( 'width', 1280 );