Customize: Allow (optional) `url` parameter to be omitted in intercepted calls to `history.pushState()` and `history.replaceState()` in customize preview.

Fixes issue where calls without the `url` parameter erroneously end up rewriting the location path to `/undefined`.

Props Christian1012, westonruter.
Merges [39547] to the 4.7 branch.
Fixes #39175.

Built from https://develop.svn.wordpress.org/branches/4.7@39574


git-svn-id: http://core.svn.wordpress.org/branches/4.7@39514 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/customize-preview.js

@@ -49,14 +49,14 @@
 		history.replaceState = ( function( nativeReplaceState ) {
 			return function historyReplaceState( data, title, url ) {
 				currentHistoryState = data;
-				return nativeReplaceState.call( history, data, title, injectUrlWithState( url ) );
+				return nativeReplaceState.call( history, data, title, 'string' === typeof url && url.length > 0 ? injectUrlWithState( url ) : url );
 			};
 		} )( history.replaceState );
 
 		history.pushState = ( function( nativePushState ) {
 			return function historyPushState( data, title, url ) {
 				currentHistoryState = data;
-				return nativePushState.call( history, data, title, injectUrlWithState( url ) );
+				return nativePushState.call( history, data, title, 'string' === typeof url && url.length > 0 ? injectUrlWithState( url ) : url );
 			};
 		} )( history.pushState );