Reset GL buffer state after functor invocation

Functors in WebView were binding to different buffers than we
assumed in the toolkit, eventually causing a crash due to improper
dereferencing in the currently bound buffer. Fix is to reset state
after invoking functors.

Issue #6666279 Native crash in Currents, mostly on Nakasi

Change-Id: I3697812d83613fffc9193daa99beea4dbf26474a