Check next elem at mouseleave in cursor emulation

It's not obvious that we want to hide the cursor when we get a leave,
it depends on the element that we're leaving to. This makes the code
more robust.

Co-authored-by: Alex Tanskanen <aleta@cendio.se>
Co-authored-by: Niko Lehto <nikle@cendio.se>

kasmweb/core/util/cursor.js

@@ -132,7 +132,8 @@ export default class Cursor {
     }
 
     _handleMouseLeave(event) {
-        this._hideCursor();
+        // Check if we should show the cursor on the element we are leaving to
+        this._updateVisibility(event.relatedTarget);
     }
 
     _handleMouseMove(event) {