Fixes issue of method 'setTooltip'
Fixes issue of method 'setTooltip'

Fixes issue of method 'setTooltip' in modules/UI/util/UIUtil.js: Excluded 'Uncaught TypeError':
```
UIUtil.js:134 Uncaught TypeError: Cannot read property 'setAttribute' of null
```
bgrozev/jitsi-meet,bgrozev/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet,bgrozev/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,bgrozev/jitsi-meet