Add _gdmData check for null

[fearistoff]

Fixes issue #461

[saghul]

That doesn't fix the real problem, which is: why was the DO_GDM action requested when there was no gDM data stored? What SDK version are you using?

[fearistoff]

@saghul

Error was reproduced with version 7.0.8 of SDK. Server runs version 2.0.10431 of Jitsi.

[saghul]

Interesting. What steps are you following to reproduce the problem? Can you do that reliably?

[fearistoff]

Error throws rapidly - about 1% chance.

User just starts screen sharing on Windows machine (mostly Windows 10).

[fearistoff]

Error keep throwing unless user close application and open again.

[saghul]

Can you try and debug the sequence of events? DO_GDM is only sent when the user picks a surface, is it possible that it gets called twice?

[fearistoff]

Unfortunately, i cant reproduce myself that. On my Windows 10 machine in my application error does not appear.

[saghul]

Bummer. My worry here is the problem is somehow being masqueraded and not properly handled.