Fix url cursor detection on Edge

_supportCursorURIs was set to true even when Edge didn't support
URIs because the fallback value "default" was used.

kasmweb/core/util/browser.js

@@ -31,7 +31,7 @@ try {
     const target = document.createElement('canvas');
     target.style.cursor = 'url("data:image/x-icon;base64,AAACAAEACAgAAAIAAgA4AQAAFgAAACgAAAAIAAAAEAAAAAEAIAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAD/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////AAAAAAAAAAAAAAAAAAAAAA==") 2 2, default';
 
-    if (target.style.cursor) {
+    if (target.style.cursor.indexOf("url") === 0) {
         Log.Info("Data URI scheme cursor supported");
         _supportsCursorURIs = true;
     } else {