Fixes errors from static analysis

[m-bialek]

Fixes three errors from static analysis:

• check if frame is nullptr before frame->Submit(); (there is a similar check on the next lines)
• initialize last_baton_ (it is used but never initialized)
• initialize client_id_ (it is set in another method but I believe it should be initialized)

[bwikbs]

I guess this is not something we fixed... Shouldn't it be submitted upstream? :eyes:

[swift-kim]

Thanks for the fix but please refer to this: https://github.com/flutter-tizen/engine/pull/218#issuecomment-990494514