Whiteboard shapes disappear in the playback page after switching video/presentation

[daronco]

To reproduce:

• Open the playback page (the responsive page) of a recording that has a presentation and shapes drawn over it
• Wait for the shapes to appear
• Click the button to switch the positions of the presentation and the video

The shapes will disappear and will not appear again unless the page is reloaded.

[alexandrekreis]

Also reported in:
bigbluebutton#3561

Fixed in bbb 1.1
bigbluebutton@ac094aa

This fix will be integrated to Mconf when we finish the merge with bbb 1.1